poll is a system call that waits for events on multiple file descriptors and also a timeout.
The way that Unix type systems handle asynchronous signals is that they terminate any long runnig system call (this includes blocking reads, as well as poll), run the signal handler as a subroutine, and let the program continue after the return from the signal handler. As the long running call didn’t complete, it returns with an interrupted system call status. The normal action of a program that is expecting that is to re-issue the call.
If nothing else is going wrong, other than the warning, the code is apparently handling that response, which suggests it is a normal condition, i.e. the thread expects to receive asynchronous events.
I haven’t looked at the code, and you didn’t give the exact version,so I can’t be sure why it would receive signals, but that reason is not going to be simply related to the format of the file.