It seems that most users have found this site through SO. Because most of the users have quite high reputation on SO. Is it?
Simply because most users on Stack Exchange are programmers. Stack Exchange started off as just Stack Overflow, a Q&A site for programmers. It's since branched out to include sites on all sorts of other topics - movies and TV, cooking, academia, and so on - but Stack Overflow still gets far more traffic and users than all other sites in the network put together. It's a reasonable guess that most of the people with accounts on Movies & TV (not necessarily active accounts) came here from Stack Overflow, and were on Stack Overflow because they're programmers.
Maybe someone with Data.SE knowhow could put together a query to actually check this. But in the absence of specific numbers, I'm going to go with "probably". Again, note that I'm talking about all users - not people who browse the site without joining (many of whom are probably film fans who found the site through Google rather than via Stack Overflow) and not people who are active site users (however we might define that).