It is a byelaw of many airports (I can certainly vouch for Gatwick) that a slide is armed during the refuel process, but as you say I have never known of one being deployed due to a refuel problem. I can also say that I have never seen any slide deployed whilst disarmed, but I have seen many slides deployed when the cabin crew have forgotten to disarm the girt bar. Most aircraft are prone to the debris at the bottom of the door, but this usually manifests itself by making the girt bar difficult to arm/disarm and would be very surprised if this wasn't noticed. The answer is, if in doubt don't touch the door until an engineer is present, then we can take the blame! Lets face it, we all make mistakes, and this was probably one of them!
