Skill issue.

Fun fact about spice tolerance. Many people think tolerance = resistance but that's not the case. After a certain point, people who love spicy foods report the same levels of spiciness compared to those who don't regularly eat it, it's just that they are used to it and even like it. So something that is a 10/10 spicy is the same level of spicy for everyone, it's just some masochists prefer it to be that way.

So when people say things like "oh that wasn't that spicy" it still usually is spicy. Their personality just prefers it that way so it doesn't bother them as much.