This usually indicates it was the first file in a sequence or captured by the primary camera lens.
Some Android file managers rename media this way when moving files between folders or SD cards. 2021-09-27_15-53-52 video0mp4
Many brands (like Vantrue or Rexing) use this exact "Date_Time" format to help drivers find footage of specific incidents. This usually indicates it was the first file
The name serves as a timestamp, allowing for easy chronological organization: The video was recorded on September 27, 2021. 2021-09-27_15-53-52 video0mp4
Software like OBS or Windows Game Bar often defaults to timestamps to prevent overwriting previous captures.