I think there's a gap between "opportunity to collaborate" and "my life is hell and you stole my idea"? If something is open source (and licensed appropriately) then even collaboration becomes moot. There are a lot of takers in the world, and not many givers.
To what end though? They’d exist at completely different ends of the technical stack to the point where it’s likely very unusable for the final product. Even though they do similar things, it’s very doubtful collaboration would have netted anything.