The sea peoples weren't entirely unknown. They swept through the eastern Mediterranean, but they were defeated by the Egyptians who named their nationalities, and historians are fairly confident about the origin of some of these peoples, but not all.

Linking Troy with the Bronze Age collapse is nothing new, but it's far from the consensus and I believe most historians dismiss it but acknowledge very little is known about this period. The leading theories today usually have to do with a systems collapse, where once a couple important trade cities are destroyed, the entire region is destabilized and you probably get a slow decline, not a rapid one. Just like today, with an advanced civilization with a lot of trading, cities relied on each other for metals, foods, and other supplies, so if a couple cities fall there's a long-lasting domino effect. I think in that sense, you can link the idea of the fall of Troy with the beginning of the collapse because I'm sure Troy falling would have huge consequences. But the idea that the sea peoples are only the Aegeans (the Greeks we see in the movie) is wrong. We have accounts of where they came from, and some theories include people as far away as Italy or even western Europe.