I agree. While they may have made an effort to control for not searching about nappies, they could have implicitly biased themselves in other ways. For example, one may have googled something similar without realising the similarity, e.g., "Baby Shark" (a popular song a few years ago) or such. In other words, nappies may be related to many other terms that they may have (implicitly) searched for.

That's why running an experiment and capturing data (of searches amongst other things) could be more meaningful than anecdote from friends if a friend or such.