As far as I know, the slot/linear salsa version came from Puerto Rico, i. e. from Puerto Ricans. Puerto Ricans are all born with a US passport. So I guess it would not be wrong to also call it an "American" art form when one talks about the national territory where it came from. However, nationality and culture are not the same thing. For me, "American" as a culture means "Anglo-American". And Puerto Ricans are definitely not Anglo-Americans but Latinos.
Puerto Ricans have always danced slot/linear salsa and for them, salsa has always been a street dance. Go to Puerto Rico and see for yourself.
Here a young kid at a street festival:
That is PR elegance!!! Makes my salsera heart leap!!! LOVE it!!!
And here young PR salseros at fiestas patronales (patron saint street festival):
It still is a street dance, not a ballroom dance. But Puerto Ricans believe in elegance. And when Puerto Ricans go out to a stylish dance to a fancy hotel, they dress to impress and look even more stylish!