Yes, that undervoltage event points the finger at a power issue. Is your mains supply unreliable? My best guess is that you had a power brownout and the voltage dropped enough to interrupt the write to the SD card, so that the SD card got in a mess. You might have seen the lights dim at the same time, although that is less likely if you have LED light bulbs.
Another possibility is that you have a loose connection in your power supply wiring. Check that the screws in the VIN terminal block of the Duet are tight.
For the future I may implement monitoring of the second power monitor input on the Duet WiFi, so that if the 5V power falls below 4.0V then the board is reset. and won't try to start until 4.2V has been reached.