I mean, possibly? Autism can indeed manifest as something extreme. And whose to say it spread evenly? Maybe on his bad day he can watch 5 back-to-back or 3 with breaks in between
Edit:
Out of curiosity I tried to search the movie duration (keyword: back to the future movie duration) and got 1h 56m.
So, 116 minute × 50.000 = 5.800.000 minutes
5.800.000/(60×24×365)≈11 years
11 years is doable in 41. 8 years before he heard of back to the future, leaves 33 years. Split the day up into 8 hours of sleep, 8 hours of back to the future, and 8 hours of anything else, that becomes 11 years of each.
He probably knows the script, the shots, the acting, the props and every other part that made it on screen better than the whole crew combined ever knew them.