I suppose a "lie" is worse than a "trick". And because the boy didn't fool people with a good intention, wouldn't the word "trick" be inappropriate?
Native speaker’s answer
Rebecca
A "trick" doesn't always refer to an act of fooling people with good intention, and can sometimes be used in the situation where there were bad intentions. In this case, it is fine to use the word "trick", although it definitely makes the lie sound more playful and less serious. So it may be better to use "lie" here instead of "trick" although it is perfectly fine to use "trick".