It is a bad argument because the premise is false, the price of stock market options over time is not invented.
Stock market options are indeed an human invention. But their price evolution depends partially on the behaviour of individual humans. Such behaviour is partially designed. Laws and regulations try do do so, but only with partial success. Part of such behaviour is also designed by individual humans or groups who make their plans as they see fit, but these humans/groups are not coordinated and the overall result lacks design; furthermore these plans are not always followed by their makers. There are also humans who buy/sell on a whim.
It also depends on natural phenomena. Good weather may raise the price of stock options for a distributor of crops.
So, the Black-Scholes equation is describing, with a certain degree of acuracy and imperfection, the evolution of the price of stock options, and such evolution has not been designed or invented.
If one claims that although a stock option was invented, the
black-scholes equation can be said to be discovered, how many more
mathematical theorems, equations, models and so forth are out there
that are waiting to be discovered, dependent on our future "inventions
We don't have to wait for those inventions. We can develop mathematical concepts for them before they have been invented. This has already happened. Boolean arithmetic is very useful to describe the behaviour of electronic computers. Yet it was invented/discovered before such trinkets where invented. And when George Bool invented/discovered boolean arithmetic there was no practical use for it. Same could have happened with the Black-Scholes equation, it is not unthinkable that it would have been invented/discovered before stock options were invented.