New2grammarIs Y second guessing?
I wouldn't say so. This is simple disagreement.
Second-guessing is criticizing someone's motives. It's calling into question the reasoning or motives behind someone's decision.
Say that a public official makes a decision. He gives money, let's say, to a charitable organization. People start criticizing, saying that the official made the decision which would bring him the most financial gain. They act as if they knew better than the person who made the decision what motives were in that person's mind. They are second-guessing the decision.
Such criticism can apply to the actions of anyone, whether celebrities, or government officials, or sports figures, or your next-door neighbors. Any time you learn of some action done and the person's reason for doing it, and you call the reasoning into question, possibly inventing various scenarios that you imagine are, in your opinion, the "real" reason they acted as they did, you are second-guessing.
CJ