But how do you know, that if kroah.com would use Let's Encrypt it would belong to Greg K-H? What if his true WEB-site would be e.g. greg-k-h.com?

Objectively better than serving 12MB of JavaScript slop, trackers, and "analytics" over HTTPS so you can share a recipe for flan.

Greg K-H has more credibility than 99% of posters here.

He's literally the #2 guy in Linuxworld (behind Linus). What have you done?