You are correct, That came with the "migrate all from ~/.gimp-2.8/ before I cleaned it out. My mistake but something to look out for.
As long as users understand where everything is.
I now have my regular Gimp 2.8 profile, a 2.9.3 appimage profile (.config/GIMP) and now a 2.9.5 appimage profile (.config/config) Something will have to go.
Still recommend this for linux users as an easy way to get familiar with Gimp 2.9 working in parallel with a regular Gimp 2.8