Now that did make me stop in my tracks, and I think I actually said out loud "What the hell?"
I have not played Portal either, but I have to say the technology in Prey was fantastic, not just using portals for positional changes, but like in the example
Victim mentions, seemlessly messing with scale as well.
So while they used the idea for different ends, I do think Prey deserved more credit than it got.... lets just say, had it been exactly the same game, but made by Valve, it would have got that credit.