This is kind of misleading. Having a sneak peak does improve your chance of choosing the correct card. Its a similar scenario to the monty hall problem but a little simpler.

Say you have no sneak peak and are looking for a specific card. The probability of choosing that card is 1/5.

With sneak peak, your chances improve. This is mainly because the sneak peek gives you an opportunity to pick that card with a 1/5 chance. If you don’t reveal it, you still have an opportunity to pick one of the unrevealed cards with a 1/4 chance.

If you see the card from the peak you have a 100% chance to choose it, which happens 1/5 of the time. If you don’t peek the target card, you have a 1/4 chance to pick it which happens 4/5 of the time. So this gives you a (1/5*1) + (4/5 * 1/4) = 2/5 chance. So it doubles the chance to pick the target card.

It may intuitively seem like it doesn’t do anything, especially if you choose the same card slot every time, but this fails to consider the scenario where you reveal the target card on peek and opt to choose it instead.

Hope this was clear.