Not going strictly by the rules--barring specific cases with their own overriding text, there's no rules basis for getting false knowledge from a knowledge check. Either you succeed at the appropriate knowledge check and know about the creature (the higher the success, the more you know) or you fail the knowledge check and you glean no information.
The rules for knowledge checks are deliberately sparse even in comparison to the general skill check rules, which are already worded such that GMs are specifically empowered to expand them. So your experience may differ--a particular GM might provide false information when a Knowledge check is failed, or they might simply say "you don't know" and let the player draw their own conclusions, true or false though they may be.
Edit: It would certainly be reasonable for an NPC to suspect that a human weretouched shifter using wildshape is in fact a lycanthrope, especially if they fail a knowledge check to know what lycanthropes are (and thus have nothing to compare against). I wouldn't worry too much about knowledge checks in that case, though--just run with the particular creature's personality and background.
Our current game has a PC gnome with a curse that left here with horns and wings. Some of the populace has mistaken her for a demon. I don't bother rolling knowledge checks for Joe Peasant in this case; I do for specific interesting NPCs whose perspective might be up for debate.