@Lynkaster You can definitely cut like that when using paring knives, albeit with decent cutting skills. You can cut away from you if you're not confident but the intent with your thumb is you still push down but away from the blade just barely skimming it. Depending on the sharpness of the blade and how competent you are, actually stop the blade on the thumb. I can do that myself on like cucumbers but I have relatives and seen them inward cutting hard materials like carrots at crazy speeds.
Anyway, liked that AV gag.