From the perspective of someone asking for Y, I've often been a victim of this because I'm met with a slew of imagined X's -- X0, X1, X2, ... an unending list of problems, often more complicated than Y -- due to their narrow preconceptions, making the whole exercise of asking someone not worth the time.
From the perspective of someone being asked for Y, yes, often I can suspect that there might be some mis-matched X there, but in order to be helpful, I try to answer Y directly and honestly, and then point out my concerns, describing my presumptions. If, indeed, the one posing the question has jumped to some invalid conclusion Y from X, then I've given them all I can. Trying to pre-empt it by telling them "don't do that!" is pointless -- if they knew where they had made an unwarranted conclusion, they wouldn't be asking the wrong question to begin with.