Looking at the sources a bit further, my previous post is wrong.
Then again, on receiving that event, the handler calls process_control_request(), which has at the very beginning a place marked with a comment as "Vendor request", that checks for a specific vendor id and sets a handler and calls tud ...

A little late to the party and not familiar with the tinyusb codebase (or usage) but..

You added your of code inside a default event handler. Presumably (based on how the function is defined) the function pointer to that handler is either entered as a value in a field of some struct used in setting ...