I wonder how many of those extra hours watched are because the stream just didn't stop after the person fell asleep. I can't tell you the number of times I've fallen asleep while Netflix played (or walked away) and it went right into some other show I didn't care to watch (and never actually did).

If hours streamed is your metric for engagement.. of course having the stream continue on its own would make that number rise. It doesn't actually say anything at all about real engagement.