As you know, the two terms mean something different, as spatio-temporal relations aren't in themselves causal relations. Being spatio-temporally isolated simply means not standing in spatio-temporal relations like “before,” “10 minutes after,” “beside,” “10 meters below.” Being causally-isolated just means not having any causal relations, such that nothing that happens in A affects B, and nothing that happens in B affects A.
So the question is, can things — and let's not talk about possible worlds for a moment since possible worlds are defined in terms of these relations — be spatio-temporally isolated without being causally isolated and vice-versa?
In the first case, some people imagine God as living in a spatio-temporally isolated realm, but as knowing things that happen in our space-time (i.e. having beliefs caused by events in another space-time). That offers an example of causal but not spatio-temporal relations. The events are spatio-temporally isolated, but not causally isolated. Remember I'm not trying to offer a physically-possible example, only illustrating the difference between the concepts.
Meanwhile, in the second case, imagine two things popping in and out of existence for only a second in the same space-time, and so standing in spatio-temporal relations. But imagine that they do not have common origins, and that they are further than a light-second from one another, so that no information traveling at the speed of light from one to the other could reach the other. I would say the two things are causally isolated, but not spatio-temporally isolated.
Remember that nothing turns on these being terribly plausible scenarios. (It may well be, for instance, that causation in our actual universe always involves spatio-temporal connection.) Indeed, the possible worlds that the concepts are used to define may themselves be a little strange! What matters is just that the concepts — these two kinds of relations — are distinct.