Actually I said controversial Jay...
Agree that getting a good key is crucial which is why I said prime it and put down a thin layer of smoothing compound instead of tiling directly onto the painted concrete.
That is what smoothing compound is for: providing a good, flat, smooth, strong key for the finished floor covering, whether it is tiles, glued vinyl / homogenous PVC / linoleum, or whatever else.
We do all those kinds of flooring, not just tiling. Thousands of m2 a year, literally, in hospitals, schools, large office buildings, as well as hundreds of wet rooms with 2mm vinyl tanking on the floor and walls, hot welded.
The advice I gave that chap will work and he will save time, money and mess.
If you want to try and talk him out of it that's fine, but please direct any further doubts and worries to him instead of me. I know that the 136m2 school library I have to sand, prime and apply smoothing compound to tomorrow in readiness to receive linoleum on Friday will also work, and that if I tried to use an 8" angle grinder it would take me until Christmas to get the concrete clean of all "deleterious or unstable layers".... :sleep1: