Social media addiction is a meme (in the technical, mind virus sense), gambling addiction isn't.
I don't know if this is what the study authors were thinking, but I see it as a bit like not taking people's word for it that they're gluten intolerant. It is a real thing and people do know that they have it, but also it's a trendy thing and there are a lot of people trying to convince you that you have it when actually you're perfectly normal.
I don't think there'd be a problem taking their word for it if the questions asked were the right ones.
Asking people if they feel like they're addicted to social media without framing exactly what you mean by addicted (and for that matter what you include in social media) might both overcount and undercount.
Have everyone who answered answered on the basis that they see this "addiction" as a problem, or a negative, and something they genuinely find hard to stop (as opposed to not really wanting to do anything about)? On the opposite end, are the ones who disagree counting forums like Reddit, or HN? Discord servers? Are they talking mostly about one one-on-one contact with friends on, say, Snapchat, that they're "addicted to" because it's social contact they enjoy, or depression-boosting, compulsive voyeueristic doom scrolling that they're addicted to in a downright harmful way?
It's a start, and little more, to ask that first question that pretty much only tells us that there is something of sufficient magnitude to probe further. To start with, the respondents appear to not have said whether or not their "addiction" is something that causes negative effects on their life or not.