I think people conflate nostalgia with reminiscing. Driving by your old high school and being hit with a flood of memories is more reminiscing about those times than longing for a return to them, which is typically what people who get nostalgic do.
For most people, they might be nostalgic for a period their parents or grandparents were alive, and it's perfectly normal missing those moments and even wanting to return to them so that you have that experience again.
But Chantal isn't just reminiscing. She's not just remembering a time back in high school where she did this or that - she is actually longing to return to that era, even if she doesn't admit it. The fact her stories almost all universally take place between a specific time period between the late 90s and the early 00s is a good example of this.
So, she is nostalgic for an era where maybe her life wasn't as awful as it is now - even if, back then, it was nothing spectacular.
The reality is that most of Chantal's stories abruptly end when she hit her 30s. Now, while a lot of those stories might have been exaggerations or even outright lies, I don't doubt Chantal was more active in her teens and 20s than she is now...even if, compared to most people in that age group, she was still woefully limited.
But that's the emotional negative of nostalgia. People who are constantly nostalgic are likely nostalgic because their current lot in life is not emotionally fulfilling. And that, above everything, is proof Chantal's happy-go-lucky, my life is awesome perspective she pushes now is just a charade. Someone who is content with their life RIGHT NOW would not spend so much time trying to recreate her past, either through mukbangs, stories or buying stupid retro candy.
And that, really, is the irony in all this. Chantal is not happy with her weight, and I'm sure with her health issues, or the fact she's seen as a joke, and circus curiosity on the internet. But she's too stupid, and too lazy, to actually do something about it - or has built it up in her head that she'll be able to figurer it all out some day and when that day comes, she'll be able to throw it in the haters' faces.
So, for the time being, Chantal will live in an era where she was more conventionally normal looking, actually had some semblance of a social life, even if it wasn't all that grand, and actually did things besides cycling between the couch, kitchen and bed all day.