I mean, it's all in those three words "biggest stomach issues".

You read it as (biggest stomach) (issues), so like, issues with large stomachs. OP read it as (biggest) (stomach issues), so, you know, like digestive trouble, and a lot of it.

I think those words are definitely a bit ambiguous, but also, I certainly read it in the second way, not the first, and it seems like most people do judging from the comments. I don't think your reading is totally impossible, but I do suspect the author of the tweet meant the other.

(Also, sorry if this is confusing, I'm a bit high. Where's the Stalin bong emoji? I wanted to put it here. Damn.)