It's not serious until they figure out what's going on - more likely than not, it's nothing at all, which is why I joke about it. NASA is taking all precautions, and the astronauts are in no danger at all right now from this - they're just going to stay up there a little while while they make sure it really is nothing harmful - no big deal. And if it is something, then there are some alternatives that NASA can use, from repairing it, to sending up another shuttle to rescue them, to who knows what. The last shuttle, they didn't think there was anything wrong, that's why they let it come down.
I'd say, let's laugh while we can - no reason to sing the dirge until someone is dead.
Had a bunch of fun with my boss, with that great headline. The UFO in orbit around earth bit is great, and NASA confirming it and tracking it really makes the impression perfect. It'd be fun if it were two little spaceships - there was a fun short story once about the arrival of aliens on earth - the landing field is ready, dignitaries waiting, communications established.... but we can't find them when they say they've landed! Turns out we never established scale, their whole spaceship is just too small for us to see.