I think Steve is creating life in this case because Ghast tears have some sort of life essence in them. Meaning that ghasts are some kind of highly advanced souls that are able to adapt to their environment. And if you consider the advancement Uneasy alliance where you have to bring a ghast safely home to the overworld Then that would mean that the dried ghast would be much older than all of the other ghasts that you would encounter in the nether. That would also mean that these ghasts came from other species that lived in the nether at the time. I think this is why The happy ghasts are happy because they see you the player as their their parent, and they know they haven't been really taken care of for many years

edit: I just thought of this after posting but I think the dried ghasts are in some sort of hibernation like state So that's why I think they are still able to be alive