First, if you have not already, do a Reset (restart) of the iPod
Learn how to reset your iPod - Apple Support
If the problem recurs... Your iPod nano can receive remote control signals from headphones that have control buttons on the cord. Even if your headphones do not have control buttons, it may be sending false signals. Make sure the headphones plug is fully inserted into the headphones jack. It should "click" into place. You can still get audio when partially inserted, but the connection points on the plug may not be aligned properly (causing false signals).
If that does not help, try a different set of headphones to see if the problem goes away.
If that does not help either, you may want to do a Restore on the iPod using iTunes, in case the iPod has data corruption. This erases the iPod, reinstalls its software, and sets it to default settings.
Use iTunes on your Mac or PC to restore your iPhone, iPad, or iPod to factory settings - Apple Support