> Seems pretty clear that he was neither aware of it being taken down nor the reason, so I think it's safe to assume that Signal didn't contact the maintainer directly.

You could be right, but I think another possibility is that the maintainer did get contacted earlier by Signal, and just didn't mentally connect the dots between that and his Snap package being pulled.

Note that I don't know how realistic this is, I'm just trying to be fair in my assumptions.