This is probably a poorly-thought out theory. But it occured to me that the Vorts might have employed Gordon in HL2. At the end of the game gman comments "I have recieved some interesting offers for your services." So, he pulled Gordon back into stasis, in a sense betraying the Vortigauts. This is how I look at it. How else would they know where Gordon's obscure location is, without employing him through the Gman (and that he is being held in stasis). Like I said, there are possibly many holes in this theory.