im having the same problem as that guy, and the thing is, i did pick the "make him your pet' option, i beat him and there was no follow up. I tried doing it a few times and nothing worked, i do think it's a bug (didnt work on mobile either)
That's weird... It worked for me, do you have maybe the proper amount of likes and hearts with him? Maybe you need to finish the event first related to the lizard tribe?
