It is so comical. I knew Witness families who watched every Disney film featuring fairies, witches, magic, genies, etc, but were mortified of the SMURFS.
I first heard it after I had left in the late 1970s - from a kind of halfway-in, halfway-out JW that I used to know when I was active. I actually thought it was a joke at first - but sadly enough, it was real in a very weird way.
This guy said that somebody reported that plastic smurf dolls were walking around right there in the kingdom hall (under satanic power) and wanted to know if I thought it was possible.
I told him that it was IMHO NOT POSSIBLE unless those dolls had batteries in them.
I am still not sure if this was ever an official WTBTS superstition, but for sure it developed an urban JW life of it's own.