I dont know who wrote this but it is incorrect grammar for American English. I dont want to steer you incorrectly so, maybe it is correct for other forms of English.
The verb form of humor is something on party does to another, for example: He wanted to explain to me how to get rich, since I had nothing to do I humored him.
It generally means you entertained (pretended to take seriously, listened etc) an idea which you did not actually believe to be feasible.
Another example: 'Look, I know you dont believe in aliens but I really saw a UFO. I have the footage, just take a look, humor me.' (pretend to take it seriously, entertain the idea, give it a chance).
I believe what the post should have written for proper American English is 'amused'.
"My dad is amused as how many people have seen this" makes perfect sense.
In English, humor almost always refers a sense of funniness or comedy. I suspect it had a broader meaning before, as in disposition but now a sense of humor means a sense of comedy or what is funny.
So the author could have also wroteL: My dad finds it funny or My dad finds it comical, or My dad is laughing . . .