Of course. In sports entertainment, "popular" has a different meaning than in other places. In high school, the most popular student is the one who's most liked. In pro wrestling, however, the most popular is the one who gets the biggest reaction; the one who gets the most response from the audience.
The guy who gets the biggest boos is just as "popular" as the one who gets the biggest cheers. I can't think of how many times I've seen folks presume that the performer who is booed the loudest must be considered the most unpopular wrestler......but it isn't true, not by a long shot.
As for whether Zack Ryder is the most popular superstar, it's subject to opinion. If you go by crowd reaction, I'd say he's pretty close to the top.
But, if Zack is the most popular, I confess to being a little disappointed in what the fans find pleasing. In other words, I think if behaving like a clown is what's doing it for Zack, then good for him for finding the formula.....and bad for the crowd for following it.
His facial expressions remind me of a 3-year-old who's just been scared by jack-in-the-box popping up. If you like that kind of thing, more power to you, I guess.