Always found it puzzling that they have London Overground employed and trained safety critical dispatch staff on the platform but they only dispatch Southern trains.
The station is operated by TfL and so the staff are TfL staff (well, employed by TfL's Overground concessionaire). The only trains that require staff despatch are the Southern Class 377s. It isn't particularly uncommon.
If they are there they should dispatch everything and then this incident wouldn't have occurred.
The other two types of train, the 378 and the 700, are driver-despatch using on-board monitors. That's not unusual either.
The working of the station has some worrying concerns as well. IMO they should have retired the ramps that were physically compatible with one class of train but did not block the door operation, it seems the later ramp could have served for both and removed one source of error.
GTR were the ones who removed the ramp for the 378 and replaced it with another ramp for the 377, though. And the staff weren't trained on the different types of ramp so, because the 377 ramp fit into the 378 lugs, they didn't know it was wrong. The only difference between the two ramps was the 378 ramp had the extended arms to prevent the doors closing.
Perhaps the 377 ramp should have the arms too, it would certainly make sense, and would prevent this happening again.
But the station working doesn't particularly concern me. The simple fact is that the driver didn't see a huge yellow ramp and a staff member in hi-viz in the gap between the white and yellow lines when he closed the doors and still didn't see them when he decided it was safe to set off.