As someone who watches a lot of Dota (at an esports bar with strangers who may or may not know dota) and plays very little, you’re half right.

In football You don’t need to know, exactly, which way the plays are going to go and why, but you do need to know the rough constraints of the game and what is physically possible to perform.

Some of the things that happen in dota are utterly impossible to follow unless you have, at the very least, a knowledge of the (on average 3) active abilities of the ~110 heroes.

Yeah, I think this is the major difference. Being from Europe I don't really know anything about American football or baseball beyond the basics, but watching a game it's pretty transparent whenever someone does something good. I don't need to know batting averages, the difficulty of plays, or why a play was exceptional to know when a player or team scored points.

Games like MOBAs are opaque by comparison. I can see roughly what's going on but I couldn't tell you if a team is winning or losing to save my life. In football if the guy holding the ball is out in front of the defending team and running to the end zone I can guess he's going to score a TD, but a team can look like they're getting whooped in DotA but really they're tricking the opponents and someone is making a sneaky play in a different corner of the map or someone has an ability or gear that means the situation is the reverse of what it appears, etc.

All of that is really only apparent to someone very familiar with the game.