SIDI, that is appalling, and it is not the first time I have heard such a thing. Children in certain religious groups, need to have better derech eretz. Certainly it is obnoxious for them to call out “Sheigetz!” to a frum Yid who has a different hashkafa from their own (but who is nonetheless unquestionably frum).
And I will be even more controversial here, and say it is also appalling for them to direct that remark to a non-frum Yid. No Yid is a sheigetz, and the expression is meant to be disparaging.