Most Astros I've seen put down earthly star before the pull so it can do a big explody during other burst windows allowing for higher damage output from the astro as well as letting that cover some of their initial healing (this is especially true for this scenario if the astro was in the alliance who's tank was main tanking previous bosses)

In general, I see far too many times people just sit around with their thumb up their butt waiting to pull in 24-man content, so it wouldn't surprise me if the astro put it down anticipating a pull only to have people just stare at it for 24 seconds, letting it explode.