Even though this doesn't sound like the hold button would have mattered, always use the hold button. I think it is especially important on small devices which can slide around or get bumped.
There is a chance you might recover that audio. Do a search here for photorec and follow the tips in that thread. When using photorec disable all file types except audio.
When you saw the mt write the file at the end of the first set, did you happen to look at the length of the file? Just wondering.