What leads you to believe that the player intentionally "hid" (doesn't that sound silly?) his skill level? In general, where is it written that a so-called good player is obliged to always play perfectly? It would be strange if a player performed well before the tournament and then suddenly played worse during the tournament. This raises questions – it's illogical. If a person "improved" during the tournament, there is nothing unexpected about it; on the contrary, it is quite common.
You have heard the expression "fan game," playing for fun.
1. A person may not be in good shape, may be upset, may have argued with his girlfriend, or, conversely, may have made up with his girlfriend, or simply may have had a few beers. There are many reasons that can affect a person's performance in a particular game.
2. A person has the right not to disclose these reasons.
Presumption of innocence, ladies and gentlemen.
I don't think this trick will work; I don't know why he decided to play, maybe to mock others, maybe he just has nothing else to do... but in the tournament, there will be NEWCOMERS playing, not players with good experience.
And who is mocking whom?
Все в ней нулево и кукольно.