Those videos are extremely hot. I agree with BulgeGuySD, that guy is using the pressure of rubbing his cock against his fly and his pants to reach orgasm. Still that's not always easy to do to and it is very erotic.
I’ve been able to coregasm - orgasm handsfree doing pullups, leg lifts and dips without any external stimulation or edging. I posted a video on here with subtitles describing what I go through and feel doing this and I'd be happy to answer questions or share info -
How I Cum Handsfree
Some people are more hardwired to coregasm than others and some have achieved them with practice. And there are others on here who achieve HFO through kegels, nipple play, or focusing on muscle movement and the energy, sensations and "impulses" in their bodies to bring themselves to orgasm. As BulgeGuySD said it can take a lot of focus, concentration and practice, but HFO's can be amazing!