Clearly being untznius in front of a goy is 100% assur as it is “pritzus”. The only exception is a nochri lifeguard, since he is a life saver. See Igros Moshe EH 4:62:1.
Where does it say Nochri in the Teshuva?
It does not, BTW.
2: Rav Moshe says it is MUTAR not Assur. He says a Yaras Shomayim should not be there if/because she should be worried that the male lifeguard will follow the female home (which even Rav Moshe says is remote). He does not have a problem with the lifeguard per say.
Did you ever actually read the teshuva, or are you just quoting (like I have called out others (the same person?)).
Still looking for a source.