To some extent the intent of the author matters, and in their "Just buy a license" pitch[1], the Qt company implicitly threatens lawsuits for GPL violations _if_ you use the open source version and fail to provide an adequate means to switch out the linked binaries. So the people who could enforce a copyright claim are drawing that distinction, which means it does matter here. In addition, they mix licenses between GPL and LGPL, so failing to take proper care means you could be relying on a GPL module and think you're ok by complying with the LGPL.
You can meet a major LGPL requirement by dynamically linking your dependencies or by providing object files that the user can statically relink. Neither is circumventing the LGPL, however.
I take your point the Qt company wants (L)GPL licensing to sound scary, so they can sell licenses.
Cargo links all the rust code together in a static binary, but the C/C++ libraries can be linked dynamically, and in the case of something like Qt, most certainly are.
Since most important part of Qt are LGPL, you can use this crate and other Qt binding crates to develop proprietary applications.
(Only if you wish to use one of the few parts that are "only" GPL, then you need to release the final product and all its parts under the GPL, or acquire a Qt license)