There is absolutely no indication in the dvd that it was Caleb's imagination, you are just imagining that it is.
If it was Caleb's imagination that was making it fly then it could also be claimed that he thinks his plane is magical. The WTBTS has gone to great lengths to demonstrate how Caleb does believe it is magical. Whereas they do no such thing as far as Sparlock is concerned. There is no indication of any magical abilities that Sparlock possesses.
The mother obviously believes Sparlock is in fact magical and this is demonstrated by the fact that she wanted it thrown out. If she thought it had no magical qualities then there would be no reason to throw it out. She even makes the point of saying 'Who likes magic, Jehovah or Satan?'. Therefore she has just taught her child a very bad lesson and that is that toys can be magical when in actuality there was no evidence of it.
How is a JW able to determine whether an item is magical or not? It would seem in this instance that it is through a 'mob mentality' perception. That is, just because everyone says it does have magical qualities it is believed, even to the point that the JW believes it is.
It is not surprising that this comes from the WTBTS as they have been teaching mixed messages for decades.
I just had my daughter watch this video as she has just undertaken a certificate in child care. Her reaction was not surprising. She said that the video presents too many negatives and this is a very bad way of trying to teach children. Presenting lessons in a positive manner is what will encourage children to behave properly. The use of the words 'hate' and 'obey', in her opinion, were bad choices and instead like and teach are more age appropriate.