Dad gets up during every movie without pausing.

My dad always does something I've only ever heard of people occasionally doing. No matter what movie or TV show he's watching at home, he will get up in the middle of it and with zero urgency, go to the bathroom, grab food, look out the window, or do any number of random things, all without pausing. He'll then sit back down having missed 5-20 minutes without saying a word and never asks questions after the movie.

It used to drive me nuts when I lived at home over a decade ago and recently I stayed over one night and watched him do the same thing. My mom doesn't even bother asking if she should pause.

Quality doesn't matter either. It could be the greatest movie he's ever seen, but he'll still miss 10 minutes of it doing whatever. I've seen him take out the garbage, cook popcorn on the stovetop, and even fold laundry in another room all while a movie he wanted to watch was playing.

This is insane right? I understand not being in to a movie and getting bored, but in my 30+ years I've never seen or heard of him sitting through an entire movie. This is the same guy who can sit on the porch for an hour or two doing nothing. I don't understand.

To be clear, I'm not trying to change him or anything. I just truly don't understand and want to see if anyone else knows someone like this.
 
*EDIT* People keep saying it's about spending time with others or not wanting to interrupt. It's just my mom and dad at home, and if they disagree on what to watch she'll go upstairs to watch something while he watches what he wants alone....but still gets up without pausing.