Your program continues running while the SIGTSTP
handler executes. Since you haven't set one up, you get the default signal handling behavior, which is for the process to be stopped.
While your process is stopped, it simply isn't scheduled for execution. Files don't get closed, nor is stopping delayed until files get closed (unless done in the signal handler).
This website looks like it has a helpful explanation of how a handler can be installed to perform some tasks and then have the default stopping behavior: