You raise a diverse range of questions, which I'll try to address in some form.
Lyotard is not really the "founder" of postmodernism, though his book is sometimes understood as something of a manifesto of postmodernism. Lyotard presents "postmodernism" as a name for something already in progress, a name which summarises what philosophers have been up to in developed industrial societies. The term "postmodernism" itself was used prior to Lyotard's book. It was possibly coined the American poet Charles Olson. Whether what Olson meant by postmodernism is the same as what Lyotard meant is debatable. Perry Anderson, in his The Origins of Postmodernity (from which that Wikipedia quote is drawn), claims that Lyotard got the word from Ihab Hassan. In any case, it had been used in art criticism and architecture prior to Lyotard. Hence, Gary Aylesworth's assertion that "postmodernism" "first entered the philosophical lexicon" through Lyotard's book is probably the most accurate way of phrasing things. Lyotard uses the word "postmodernism" to characterise a range of philosophical views that share certain concerns.
When, in the interview Wikipedia cites, Lyotard says that he had a "less than limited" knowledge it should be read, in part, as something of a joke, similar to what he explains in the introduction to the original report:
the author [of this report] is not exactly an expert; he is a philosopher. An expert knows what he knows and what he does not know, because an expert knows what knowledge is in his game. By doing me the honour of addressing his order to the philosopher that I am, the President of the Council of Universities with the Government of Quebec obviously knows that I do not know what knowledge is in the most developed industrial societies [(this being the subject the report was devoted to)]. He simply asked that I question it....
Les problèmes du savoir dans les sociétés industrielles les plus développées, p.2. (My translation)
Lyotard here is having a bit of fun (indeed, he is explaining, in the introduction, why the report is a failure): he has been asked to produce this report but "obviously" it is on a topic he is not an expert in. Nor is such an expert what is required; after all, an expert already knows what knowledge is but can only tell you what he already knows, because an expert's notion of knowledge is only knowledge within a certain language-game (Lyotard makes fairly heavy use of Wittgensteinian "language-games"). Instead, the report is written by a philosopher because what is required is not expertise, but a willingness to question which is foreclosed to the expert who already knows what knowledge is and thus has no need to ask.
At one level, this is just fun and games (and Lyotard's language in the passage cited above is quite over-the-top), but it also establishes a serious point: there isn't just one mode of knowing, but several; there isn't just one way of responding to the demand that prompts Lyotard's report, but several. In some ways, this has been well-known. Traditionally, from Plato and perhaps before, philosophers have argued that philosophy is different from expertise, and that what philosophy aims at ("wisdom") is superior to expertise. While making something like this first move (philosophy is something other than expertise) Lyotard doesn't try to make this second move; there are different forms of knowing (expertise, philosophy, etc.) and the point is to attend to these differences. Expertise is not required because "knowledge" is no longer understood as a single thing; rather, there are a range and variety of "knowledges" depending on the language-game one is engaged in. It's this distinction between "knowledges" and the transformation that it produces in our notion of "knowledge" that is the subject of Lyotard's report, not "the influence of technology on the exact sciences" as Wikipedia claims. (Despite the citations, neither of Wikipedia's sources reinforce this claim; Bruneault claims that Lyotard's report was written on the legitimisation of scientific knowledge and Perry speaks of it as dealing with "the epistemological fate of the natural sciences," p. 26).
Despite the occasional humorous tones, postmodernism isn't just jokes or parodies. Where they are used, they are in the service of more serious points, but with the conviction that how a point is argued can be as important as what is argued per se. This is often seen (as with Lyotard) as an implication of a consistent application of speech-act theory: arguments aren't just formal propositions; they should enact what they theorise.
