I think he might be talking with them telepathically or something.I dont think we can safely say its canon until we get confirmation. But it surely gives a lot of interesting info.
Why is he with the vortigaunts now?
It's a twitter account Liadlaw(lead writer of half-life) had, he's said it's kind of like his own fanfiction, but the way it's written and the stuff it reveals about the universe makes me want to have it as canon. The whole thing is about if breen survived by being moved to a host body(advisor) and it gives some interesting information about where the advisors came from and stuff... BreenGrub?
I remember seeing something similar on YouTube and if I'm remembering this right - and I might not be - it was basically somebody who pointed out that killing Eli in the first game by giving yourself a weapon early triggers the opening of the locked door that he's supposed to unlock for you, so they then made the leap that Eli has to die for the door to open, so therefore HL2 can't be canon because he died in Black Mesa? But it was just a joke video, because Eli isn't supposed to die, he's supposed to manually unlock the door for you and then send you on your way. Having the door unlocking also triggered to his death is just a gameplay failsafe in case you somehow manage to get him killed before he opens it, so you don't get stuck.I think Ive read somewhere on this site that whole HL2 is non-canon