the closest comparison i can think of is like the mp3 patent situation. Up until this year you were free to use LAME non-commercially even though its technology was covered by patents held by fraunhoffer & thomson.

even though vue's api is different from react's in lots of significant ways, it's not really clear that vue doesn't infringe on some of facebook's patents anyway (at least i don't know what the patents are) but the impression you get from reading every single post by an ex-fb (or current) employee is that using other react-like library put you in a similar legal situation as commercial users of LAME: while it was highly unlikely that facebook would take any action against your hackathon heroku app, it was never clear that any of those libraries (or their users) were free of actual risk. At least users of react were assured they weren't going to be sued regarding any of those vdom patents held by facebook.