Its a lot easier to sit, think and write about it, than decide in the few seconds you had available.
However, I think I would immedialtely hold postion, and be ready to escape off the runway in case he fouled up.
It also depends a bit on the runway length (and maybe its width?), but I guess if you had just landed (normally) and were backtracking, you must have been within his proposed landing area. Given that, I think I would move to the side and would have made another call repeating the runway was occupied and that there was no space to land.
I'd still keep plan B to escape off the runway though.
A quick (make that long!) word on the ground would seem highly appropriate, as well as the "reg" and a call to the safety people - maybe. Given the low fly over as a precedent, it doesn't sound like you would be talking to a responsible person, does it?