He was a Chief Tech because of the 1946 Trade Structure, which introduced, inter alia, the dreadful aircrew ranks of IV, III, II, I plus a P, N, G to denote trade.
The structure also split ground staff into two groups: a technical bunch and a admin/general service bunch - the techs were J/T, Cpl Tech, Senior Tech, Chief Tech and Master Tech.
In 1951, it was changed again (mainly for aircrew) but people in the ground trades did not revert to the original rank styles until 1964 when it all changed again, so I went from Aircraftman 2nd Class to acting pilot officer overnight (pay didn't change much though!)
Old Duffer