They gave the example of the verb yiwei in Mandarin. If you say “ta yiwei X” it means “s/he thinks X” with a strong connotation that X is in fact false. The Spanish equivalent is supposed to be the verb creerse [1], like if you say “Juan se cree que lo van a ascender” it means “Juan thinks that they are going to promote him” but with a strong connotation that he won’t in fact be promoted. English doesn’t really have a verb for “think” with the connotation that the belief is false. The claim (for what it’s worth, I am skeptical) is that English speakers are slower to learn the concept that someone can have a false belief, because English lacks such a verb.

[1] according to https://ojs.ub.uni-konstanz.de/sub/index.php/sub/article/vie... for example. I don’t know enough Spanish to say if the verb really works this way. Verbs like this are called “contrafactive”