I was farming in Rockhorn Summit and suddenly a portal appeared and Arcane Deary

[schrodinger's cat]

It's the first time ive ever seen Arcane Deary randomly appear like that. It was a cool surprise. Should i have clicked onto the portal? It took me a second to realize what was happening, but in that time he said, "I wish I can stay" and he vanished and both him and tho portal were gone.
Does anyone else have any simular experiences? Im not using an arcane deary ring (i do have one and i love it). What caused him to spawn?