This precisely.
I don't think it's ungrateful to be angry at somebody for their promises ending up unfulfilled.
Keyword being, of course, "promises".
JustPingo promised way more than he could actually deliver on three occasions now:
The "Hidden" Ninjhax Kernel exploit, SNShax and now KTM.
It's one thing to go 'i might be onto something here relating to x and y, but i can't promise anything, stay prepared by doing z' and it's another to go 'GUYS, LOOK, I'M MAKING A THING AND IT'S DEFINITELY HAPPENING!'.
The latter one just builds unnecessary hype and that's not something you want if you're not absolutely confident in what you're doing.
To summarize, it comes across as the effective equivalent of that kid whose uncle works at Nintendo and is gonna be bringing the next Pokemon game over during breaktime (with a slight twist to it): Even if it's true that your uncle DOES work at Nintendo and you DO already have the next Pokemon game, if you don't deliver at all, people are going to be pretty precisely pissed.
I don't know about other people, and I'm not even mad myself, but I'd say what people are angry about isn't not getting what they were told they would get: It's the fact that this sort of attitude is, sorry to say, very little to nothing short of being a straight-up attention seeker.