Maybe US machines are different to the ones in the UK. In the UK you don't just press a button or pull a lever to spin, you have multiple buttons that allow you to "hold" a wheel and stuff like that.
Say you have fruit-fruit-bar. You spin and get bar-bar-jack. You can roll the emulator back and repeat the spin, you always get bar-bar-jack because the PRNG is deterministic and not based on timing. So it looks like if you hold the original bar that you had, you should get bar-bar-bar and win. If you do hold it, the machine has already decided that you are going to lose this one so produces fruit-bar-bar or something so that you lose.
The display is supposed to make you think that if you had just held that bar you would have won, but it's a lie. You were going to lose no matter what, it's just trying to make you think you have a chance when you don't.