But why print it if I set the verbosity slider to 'Display no messages'
Because we think verbosity to 0 shouldn't even exists.
It's another of the many feature added only because users asked, but it still gives us so much trouble, because of users not seeing anything ( for example the request to start the APU in some planes, otherwise pushback won't start ), because they set the verbosity to 0, then contact us or simply assume GSX has "a bug", but in fact it was trying to tell something, without having a chance to be seen.
Since that message is not stopping the operations if you don't read it, we might remove it at verbosity 0 in a future update.