they've done it before with other characters. off the top of my head:
- Random elf prisoner turns out to be the princess of the elf kingdom
- random story about an adventurer who made it to silver rank makes a reappearance in the vampire kingdom arc as their guide
- Lucifer's drinking buddy now has a daughter and for some (still unexplained reason) he recognized lucifer in his child form (but not as lucifer). As if they had met before in that form, at least thats what luci speculated
- The butler of the noble they were supposed to meet back in the beginning of the vampire arc turned out to be the missing husband first place in which lucifer lived/worked
- The random beastman alice fought at the harbor when luci was still a child turned out to be the king of the beastmen
It just seems to be a recurring theme at this point with this author to give random characters a significant background. They are probably making it up as they go along but it's a non-issue for me anyway. Better than the blatant retcons they've had