Even from a distance, Halligan bears little resemblance to an ordinary human being. The ridiculous gait, the appalling lack of style, the unmoving face — just about everything makes him seem either like one of those aliens he used to read about in his spare time, or just an extremely strange parody of homo sapiens.
And, most importantly, he is not at all embarrassed by Steve's posture. Normally, when people see him hovering over a chair, they run out of the room screaming or whispering words of prayer. But to Halligan it seemed natural, as if it were meant to be. Of course, in his paradigm, killing a man for his last pennies was natural, and even stealing scissors — scissors, for God's sake! Steve could have finished him off on the spot for that alone, as well as for randomly invading the office with stupid questions...
But no. Halligan is annoying, but he's also one of the few people who has accepted Steve for what he is.
And, frankly, the only one.
Perhaps the time will come and Halligan will reveal his true nature to him. In the meantime, all that's left to do is hover and watch.