Honestly, (not knowing about this case specifics) I don't think even copying Camus or de Broglie passages (not an entire text of course) is much of a problem to be honest. At one point some things become more or less common sense or public domain. I think this would be rather than plagiarism "citation misbehavior" -- i.e. failing to cite or mention previous work. Like, not every math geometry paper needs to cite Euclid, you can just talk about triangles; or even copying passages from say the parallel postulate or whatnot, when actually delivering something novel, should not count as fraud or plagiarism, simply failing to cite a historical source, in my opinion.

Also, I believe citation is usually limited to prior written work. I don't think citing personal communications is mandatory, but at least for me lots of ideas come up in personal communications, random discussions, etc.. I think actually we should give more credit in this case, but it shows that attributing fraud for failing to cite may be a little too harsh. Again, I don't know if that's the case here, or if his thesis is just some pastiche or prior work without any significant or original contribution.