> A license is "GPL-compatible" when code released under its terms can be used in a GPL-licensed project.
Correct.
> using any GPL-code, no matter if linked statically or dynamically, requires the author to release the combined work under GPL.
Yes, the combined work itself ends up being GPL [0]. This is similar to making a fork of some BSD-licensed code and adopting the GPL for the fork. Your code, treated independently of the combination, may still be released under a (more permissive) GPL-compatible licence (like the BSD licence) if you so choose.
Put another way then, if Qt were only made available under the GPL, it would still be fine to release your Qt-powered application code under the BSD licence, but it wouldn't be possible to make a proprietary fork of that BSD-licensed application code, as you wouldn't then be permitted to link against libraries released only under the GPL. (I'm ignoring commercial licensing of Qt, of course.)
[0] https://www.gnu.org/licenses/gpl-faq.html#WhatDoesCompatMean