In Kiddushin 41b, the conduct of eating in public is likened to that of a dog. By “public”, I think Chaza”l had in mind eating while browsing the outdoor, public market place, as opposed to, say, eating in a restaurant. Although a restaurant is more “public” than one’s home, at least it’s an enclosed space. That leaves open the question of “al fresco” accommodations popular in Europe, though I suppose one could justify that as “minhag hamakom”.
A more common activity in our day is walking about drinking from a water bottle. Is that something Chaza”l would have rallied against or, perhaps it’s to be considered more urgent for one’s well being, especially in hotter climates? Then again, since the practice is so commonplace in our day, perhaps it’s not considered uncouth behavior at all.