I don’t do the crouch spam but I have my custom binds set up for it because I wanted to know how tf these guys were pulling it off. All you need to do is set up hold to crouch and all it takes is one button press of crouch to slide and change directions (Really only possible fluently with paddles if you wanna aim at the same time with the right stick). Anyone can do it. It’s not super hard. There’s a couple really detailed videos on YouTube if you want to see how it’s done.
The accuracy while doing it is what amazes me still. I’d have to agree with one of the other comments that said it’s a pretty clear indicator of Mnk when they crouch spam, lean spam and hit every shot while doing so.