Any move that could potentially do anything to mess with another Pokemon's item will always fail completely in raid battles, not even dealing damage--regardless of what the target is. For example, they don't want people using Thief on their "teammates" as a means of permanently stealing their items, because unlike Battle Tower battles, any items lost during a raid are lost forever, and instead of treating it like a 60-power move with no side effect, they go even further to discourage its use by not even letting the user deal damage, no matter if they intended to hit one of their teammates, or the boss who won't always be capable of having an item.
Bug Bite can only mess with an item if the target is holding a berry, at which point it's supposed to be stolen and immediately consumed, but even that remote possibility is enough to classify it in the "Do not use moves that mess with items while you're playing a raid, got it?" group, so that it fails without dealing damage, again regardless of who you're targeting or whether they even have a berry at all.
