I’ve used it a lot for reports when I went to university, but for short notes I would prefer markdown and for a few pages or documents where formatting is trivial I still find it easier to use LibreOffice or word. I find it likely that most high schoolers would find it easier to use word for any document than LaTeX which they probably have never heard of and would be unable to get support for unlike word which is commonly provided by the school. So while understand where you are coming from, I don’t think the students are in a situation where that would be a plausible solution. Especially due to the many pitfalls and the learning curve you have to get through for using LaTeX as efficiently and for as complex formatting as they already know how to do in word. LaTeX has a way higher ceiling of quality, but the floor is also much lower for those new to it and without the drive to learn it.
As a Dane I’d guess they didn’t realize Americans use it as a greating and so assumed you to be initiating a conversation unrelated to ordering, possibly with bad intentions.
It would be a little like starting the conversation with a “how is your mother”, it would signal way more familiarity than was had, come way out of left field and be generally unwanted when you are working if you don’t have time to stop for the conversation that would ensue.
Don’t get me wrong, I don’t think you did anything wrong necessarily, it’s just a cultural difference that likely causes misunderstandings if none of the parties are aware of it. I’d liken it to a Eurpean going to a restaurant in the US, not tipping anything and how both parties may feel the other party to be rude after the fact if the server let their dissatisfaction show.
I could of course be wrong and they may just have been an ass, plenty of those in tourist heavy areas for sure. Just something to consider if it could have been the case.