A: For Actions like this where multiple things happen, all those results are considered to happen simultaneously (Except for Actions which invoke the utilization of other cards, like Draw 2 and Play ‘Em, where each card played is considered separately, though the whole thing is still considered one “Play”).
Looking back on this, Andy realized that we could have avoided this confusion by simply writing the results in the other order (Discard the Goal, then trash all Creepers in play). We hope to tweak this wording on a subsequent printing.