It is a good question, the man says you can not enter the vault of glass alone, he also says no one was with him, but he was not alone! He is a man of mystery, i want to find out more about him, he was some sort of early explore/fighter, with out him no one can raid the vault of glass, the vault of glass is where the vex control time, they do time travel and also morph reality , that is why The Gorgon in the vault of glass( the sneaky part) can look at you and you die, they erase you from time/existence .This Kabr dude made a shield out of one those Gorgons, that is bad ass!

One theory I keep seeing is that when Kabr entered the vault, there were other guardians with him ( my guess would be a Hunter and a Warlock, which would explain the other classes raid armor in the vault ). But then gorgons erase the other two from existence before Kabr can send word of what's happened in the vault to Pahanin. Kabr is alone, but he knows he must have had help to enter the vault. " no one was with me, but I was not alone. " Idk my personal theory is that it was a past, present, and future versions of Kabr that opened the vault, since time and space begin to fray at the VoG. As far who he is now, I think he was either absorbed into the universal vex mind, or just a part of the relic he poured all his light into.

You are genius, this part is pure "present, and future versions of Kabr that opened the vault, since time and space begin to fray at the VoG." Great idea!