If you mix lies with a bit of truth, people are more likely to believe you. Because it confuses them into thinking that, "Because you know 'this and that', and we know for a FACT that 'this and that' is true, then the other things you say must ALSO be true!"
I think he bases a lot of his fakes on vaguely revealed Pokemon. Like the one in the daycare, or those from the musicals, of which we have only seen a small fragment. Making it seem more believable. And confusing people into thinking he knows everything.
And I would say it's working. Because people do seem to be getting a bit confused. Most who believe him seem to think he revealed the image of the cat before it aired in a commercial for example. And try to pass this off as proof that he is speaking the truth. While the commercial aired several hours before that, so that really doesn't say anything one way OR the other.