"Coincidental" means random, with no causal connection being explicitly claimed. It just means that two things share some characteristic (such as being relatives.) The thing that is coincidental is that the person who founded the company being discussed is also the father of another person who current events have brought into prominence.

It's why you would say something like "more than coincidental" if you were trying to make some causal claim, like one thing causing the other, or both things coming from the same cause.

So, "What is coincidental about that?" is a weird question. It reads as a rhetorical claim of a causal connection through asking for a denial or a disproof of one.