[A_C_Slater]

If 1000 winning players cash out everyday then probably at least 300 of them are going to endure a downswing afterwards. Of course, they would also endure one had they never cashed out. And for losing players the number will be over 500. So your friend is probably only one of the 300 (or more likely 500+) players out of 1000 that will go on a downswing after cashing out.

So out of 300 players a day that's 2100 a week going on a downswing after a cash out. And of those 2100 probably at least 10% think it's because of some kind of rigged cashout curse. And that's just from the winning player sample. Though if they believe in cash out curse they are probably marginal or near break-even winners. So out of those 210 players per week you will get probably a couple dozen posting on the various poker forums about the cashout curse per week.

So what I'm trying to say is that it's all just a coincidence.