1. Is it permissible to eat vegetarian food offerings from a temple offered by a non Muslim friend?

2. What is the logical explanation from considering non muslims as najis and their wet hands make things najis too?

1) There should be no objection to it as long as there is no imposition upon your religion.

2) The rules of Allah are takleef, thus, we don’t always know the reasoning behind them but follow nonetheless. In this case, it may be their denial of Allah and faith that makes them in that state.