Firstly, you are confusing patent system and copyright in your answer.
Secondly, nt's not about legality of open source license at all.
LGPL or GPL does not burden Qt Company with license obligations since it owns the source code. There is another contract between KDE foundation and QT company that we are talking here.
Don't worry, I also studied law.
What The Company can or can't from this contract is not granted unless you have supreme court judgments for the points in question. Otherwise the current patent system, which is primarily based on bluff and blackmail, would not work. As long as there are companies that would rather settle than defend themselves in court, The Company will find a way to stay in the game.