However, that was not the case. Upon further investigation and some help from other mods , it appears that Community did not want to protect it because two of those posts were from deleted/destroyed users.
Presumably, this is not the intended behavior since those two users were automatically deleted by the maintenance script. This problem was brought up before but the accepted answer there says that spam deletions count towards the threshold.
Do (should?) deleted answers from users who have been auto-deleted count towards the auto-protection threshold?