The point Comodo guy is trying to make is they invented/own the 90-day certificate, or specifically the magic number 90.
If they actually do he has the moral right to be upset (but of course that doesn't mean trademark law or common sense stop being applicable to the words "Let's encrypt")
Seriously? Even the US patent office would balk at an application to patent 90-day trials or 90-day certificates. Also, Let's Encrypt isn't doing trials, so patenting the first wouldn't even make sense.