Re: your suspenders of disbelief becoming unhitched....
You will learn how the alien knows English in the next part of the
two parter. (Hint: after all, he's been there for a long while, in a
high-tech machine...you'd think maybe he could monitor transmissions.)
I don't think the Sinclair or Ivanova did automatically believe him;
but they also had no real reason *not* to believe him. And granted the
place was going to hell, quakes and danger. He wasn't armed, he seems
rather sick, had to be helped away, almost carried...they won't turn the
station over to him, they'll keep him isolated on the station, but there
was no reason *not* to try and help him.
How do you know he's a good guy? You don't. But he wasn't exactly
imprisoned in that thing; it was a support, more than anything else, as
was shown by the fact that they were able to get him out fairly easily.
(And yes, your first guess was correct, it is a life support gizmo.)
Regards to your suspenders.