Audio file opened by itself?

This morning I woke up to the alarm on my phone, as I snoozed it I noticed that the Total Commander player had a notification open, with an audio file open but on hold. When I tapped on play I got the Total Commander warning about Stagefright and asking me to confirm I really wanted to play the file, to which I answered no. In the process I unfortunately also involuntarily closed TC before I could fully see what the file being played was, but I noticed it was from a fsck.k9 folder (so like an attachment I guess). However I haven't received any audio files in attachment in the last few days and data, wifi and bluetooth were all off during the night. I have done a scan with Bitdefender which hasn't evidenced any malware. I haven't installed any suspicious apps recently. Any ideas of what could have happened? Edit: Android 5.0.2 on a Moto E Edit2: I do use K-9 for email (hence my reference to audio attachments)