What do you think that it really was?

Bean comes qickly to the assumption that she's saying, "You promised not to kill Bean," but I find that hard to believe. Not only is Bean a very unreliable narrator at times (at least in Ender's Shadow) but Achilles' own internal thoughts suggest that he saw Bean as respecting him, the only one to know he was dangerous. (Though if we're talking unreliable narrators, whew...)

Bean wavers a bit, but ultimately stays sure that this was what she was doing, but I still feel like they're are other more likely promises.

There are a lot of reasons the given answer doesn't fit, so I'm curious what you all think!