But the point is, typically when a product is branded with a title that isn't related to it in some way, it's a sign the people making the product don't have confidence enough to let it stand on its own merit.
So if the Publisher and Developer think they can't sell this thing without adding a brand name too it, and one which at the time had very little cache with the players of FPS games, well, lets just say it usually means; "something is rotten in Kislev."
I've stood by a lot of weird directions for established series to go (Dynasty Warriors Gundam, Battle Isle: Infestation, Tenchi in Tokyo), but usually there is some context for it to travel in that direction (except Tenchi in Tokyo, that was.... interesting). But a 30's set Alien invasion FPS with cool aliens that look like the Angels from Evangelion.... and don't get me wrong it looks very cool, isn't what X-Com is.
You have to remember, games though an artistic medium, are like movies, they are products to sell and if you can't market it for what it is, you slap a name people recognise on it (ala; Troll 2... I need me some of that Nilbog milk).
That said, may not be X-Com as I know it, but my god did it look damn cool.