It's easy to guess the cards that were just laid face down, if you happen to catch a glimpse of them—perhaps in a reflection—before they are put down, or as they are being put down. This makes a pattern of guessing 25 previous cards in a row extremely suspicious. If somebody had genuine miraculous powers, or whatever, it would be bizarre and arbitrary to guess the cards shifted by one like that, deliberately inviting strong suspicion of fraud for no reason when it ought to have been just as easy, for real miraculous powers, to guess the cards as they came up. If instead someone were a fraud, however, then noticing that the cards are briefly visible as they are being put down, and exploiting that to produce a fake miracle, is exactly the kind of thing to expect. So this story of the cards really makes this Sherwin guy look like a scammer, and the people that believe in him look gullible.
Alas, it's quite common for people who do fall for simple tricks to be reluctant to believe that they might have been duped, to the point where they will swear that there was definitely no possibility at all for the guesser to have seen the cards, even briefly, before they were placed face-down unseen. They may well swear that with more certainty than anyone would normally have about a card trick, even if in fact they were quite careless with their cards at the time, since each time when they put a card down, it had been a wrong guess, and therefore seemingly unimportant. The fact that the cheat is embarrassingly obvious in hindsight only makes it harder to admit that one could have fallen for something so simple.
I believe I read Penn Jillette somewhere explaining that the real reason magicians never reveal how their tricks work is that most magic tricks are infuriatingly trivial once you know how they work. Very few are clever illusions that still seem cool once you know. Almost all just make you feel horribly stupid for not seeing the way the trick worked immediately. So it's not that revealing how the thing worked would remove a childlike sense of wonder, or anything like that. It's that it would make people angry. People don't mind being mystified by a brilliant illusion but nobody likes being played for a fool.
Magicians keeping secrets aren't sustaining a naïve belief in real magic as opposed to clever illusion. They're sustaining a naïve belief in clever illusion as opposed to trivial tricks.
I was a teenager before it was cool.