Why do you want to retrain the poor guy? If all the fuselage is covered with deicing fluid on take off run due to the wind it will run back? APU intake doors are opened so it sucked a bit.
Notice I said "if".
If someone is doing something wrong, then they need to be corrected. The point of an ASR is to find out what happened and why it happened. Once this has been done, appropriate changes can be proposed or enforced to improve safety.
We don't know exactly what happened in this case - it might be an aircraft design fault, but I doubt it. However,
if too much fluid was sprayed, or fluid was sprayed where it shouldn't have been sprayed, then this information needs to be communicated to all people concerned to avoid a potentially fatal accident in the future.
Sometimes, fluid dripping down from the fin will run around the fuselage onto the APU inlet. The Airbus APU inlet is on the underside of the fuselage and has a 'fence' around it, so any fluid reaching it from above will be forced to drip down away from the inlet. We also do not take-off with the APU running. I don't know much about the Boeing APU inlet design, but the ones I have seen are on the side of the fuselage not underneath, which might make it more susceptible to fluid ingestion? I don't know.
By the way, when we, (a UK operator) deice, we don't spray "all the fuselage", just the wings, horizontal stabiliser, fin and rudder. So that might have been the cause of the problem in this case.