The issue is your wording. Qt's model says it's licensed under the GPL/LGPL for anyone who wants to use it under the terms of the GPL/LGPL, whether for commercial or non-commercial use - or you can contact them for a license to get out of that.
The issue is that if you say "it's GPL so long as you don't use it commercially", that's not actually the GPL (which never mentions the commercial/non-commercial distinction), and users/developers can't combine your work with GPLed work.
The issue is that if you say "it's GPL so long as you don't use it commercially", that's not actually the GPL (which never mentions the commercial/non-commercial distinction), and users/developers can't combine your work with GPLed work.