I think it having something to do with getting there wish makes more sense than it being under orders. Everything else we've done so far has been about our choices - why would something as important as this not be?

Also, HK-47 was a liar, so I don't know if I'd believe him, honestly. He claimed not to have gotten any instructions to kill, the night before the execution, and then suddenly started claiming he had them when everyone was listening?