No. Your reading of it is unusual, in most contexts. It almost always means “agreement, and I have nothing of substance to add”.
It can be rude if the thing you’ve said should warrant a substantial response. Like if you wrote “my brother just died in a car wreck”, a thumbs up (or probably any emoji) would be an inappropriate response. Heavier stuff warrants whole words.
But if it’s like “Can you get cat food at the store? The kind we always get” then a thumbs up is an acceptable shorthand for "yes, I understand and commit to this request "
If those Internet duds that get mad about black people in video games spent like half that energy being mad about, like, wage theft, we’d be so much better off.