Online chats and customer service like that have to be annoying, there's no face to face or verbal communication, so people tend to showcase even worse entitled attitudes in text form like that because the communication form itself gives them hubris to hide from direct visceral reaction to bad attitude.
Americans in travels are super talkative/social as heck, generally overly nice peeps, mostly superficially but warm social habits for sure. I meet people from all over the world on the regular, and americans (generally almost allways white peeps) social habits reminds me of africans, south europeans/south americans (the type of social cultures who would invite you home to family dinner after 10 minutes convo), generally more open with random peeps. Tho sounds like you met a dude on a mission. If he is there to make a living in new place, its good practice to meet new people and network immediately.
And the chinese tourists are truly everywhere, and they are rarely ever pleasant to be around at all. And I mean them as tourists, just horrible. I worked with chinese peeps here in sweden and they like anyone else. But something about them as tourists just is so off, like its the rude country bumpkins only ones traveling (which doesnt make sense, since vacation overseas is expensive, so mostly middle to upper class chinese).
Rest of the nationalities you mentionned are geographically or culturally close to Serbia, so it makes sense, and and theres no country you wont meet a french tourist. But scandivavians/swedish in Serbia for travel is a rare thing for me to hear about. In balkans in general its becoming more popular as destination in sweden, hear plenty who go to vacation spots in Croatia, Bulgaria, Montenegro even co-worker who went to Albania this summer. But rarely ever hear Serbia. But it makes sense, all the balkan countries I mentionned have coast lines while Serbia is landlocked.