There's a world of difference between that and Thompson's attack. You don't exploit the kernel code: you exploit the compiler code, such that every program it compiles (a) is compromised, and (b) is incapable of detecting the exploit in programs compiled by the same compiler.
That's a completely separate issue. The trusting trust bug requires you to convince people to use your compiler binaries. The thing you're talking about just requires a patch to pass code review.
It's more work - you have to figure out a sneaky bug and write a legit looking patch - but anyone can do it. You don't have to be in a position of power already (e.g. being the Debian GCC packager) so overall it is much easier.
I think they only got past a single reviewer and counted that as success, none of their harm code made it into the kernel proper. However the University also committed thousands of automated "fixes" for linter warnings that weren't part of the study and the kernel maintainers ended up reverting all of them due to the Universities overblown claims.
