I'm a little in between with this...
Personally I can't help wonder if we're not talking about a bunch of people who saw their long aged software being used and then smelled easy money in the making. And I'm not too sure they have any legal grounds either, it's the same with music: after 30 years the copyrights basically drop and it becomes public domain; open for everyone to use. Even if you're using it to make money for yourself.
Now, I do agree that the company in question seems a bit weird, blaming stuff on someone who has long left, but I also think it's fair to note that we're probably not talking about a multi billion company either. So I can imagine that mistakes can be made, or that they make stupid remarks because they're not sure how to handle the situation.
And that's the other side of the medal: if you get into these kinds of things you should be prepared. Study this, do your homework and if you do get called out have your statements ready so that you at least leave a solid impression instead of that of a bunch of goofballs.