I am not so sure.
He is speaking to someone half his age, the two behind the counter might think that he is trying to chat one of them up! He has put in some effort so he could be some kind of a stalker! He went to their coffee shop especially to speak polish to them instead of just going to the place where all the other english speaking people go. He is taking it too seriously also which means that he could be crazy as fck, if he was having a laugh with them and not being so serious it wouldn't be so bad.
The only way to do this correctly is to have a laugh with the two behind the counter otherwise he can't but appear silly. Being too serious and making such an ase of speaking polish is just asking for trouble, but also speaking good polish may make him seem even more mentally deranged, to put so much effort into speaking Polish just so that he can order coffee from them.