Y far would be full fare economy. But in FT, it is used when talking about class of service to refer to economy, with whatever fare. The FA would have no clue what fare you paid. In fact I was in J, but seeing me in the economy (Y) cabin, he must have assumed I was an economy (Y) paying passenger.
My friend said that they are rude to anyone in economy (Y), regardless of the fare (they have no clue. You might be paying 3k$ and be in Y or 300$...