Every desktop machine that gets patched via the PDQ script gets the same package. This package includes a command to bypass the bitlocker screen upon restart after the update is received. On occasion an unattended computer may not have bitlocker bypassed and it will time out and shut down.
If the machine restarted, that is an indication that it received the update and that it also received the Bitlocker Bypass command. The script is set to bypass bitlocker 5 times in case there are updates that are dependent on a previous update in the same package being applied. In this case, it will reset the machine after the dependent patch is received in order for the previous patch to take effect. So, if there were more than 5 dependent updates in the patches being applied, it could have exceeded the 5 Bitlocker Bypasses and shutdown.
The occurrence of a machine shutting down because of bitlocker not being bypassed is rare but could also be caused by power fluctuations or other unknown circumstances.
Have the user restart the machine and check for a completed restart and that it functions normally.