Respawning in the Nether after dying, despite not using or having an anchor nearby

Player is respawning in the nether after dying, despite not having used or there being a nether anchor nearby. This happened to the same player 3+ times in a row.

To reproduce: Die in the nether

Expected result: Player respawns at their last set spawn point/at world spawn in the overworld

Actual result: Player respawns in the nether