No, you (and most folks here) have not understood the full picture. Only the C ABI is relevant here and not the language (C/C++/whatever) itself.
You have to know how exactly asynchronous callbacks registered with the kernel get called, how their stack frames get setup, how kernel writes to local variables within a stack frame of a user thread, how stack frames are adjusted when a blocking system call returns to user space and finally, how and when exceptions (in any language) mess up the above when they implement a different flow of control than that expected by the above "async callback kernel api architecture". All of these are at play here and once you put them together you understand the scenario.
You have to know how exactly asynchronous callbacks registered with the kernel get called, how their stack frames get setup, how kernel writes to local variables within a stack frame of a user thread, how stack frames are adjusted when a blocking system call returns to user space and finally, how and when exceptions (in any language) mess up the above when they implement a different flow of control than that expected by the above "async callback kernel api architecture". All of these are at play here and once you put them together you understand the scenario.