This can’t be right! Croyais is past tense, estás pensando does not match tense wise.
As I don’t have the original sentence of this, I can’t really confirm that it is wrong or not.
But as a matter of fact, this French sentence can be translated into English as “What did you think?” or “What did you expect?”.
The orignal sentence on tatoeba is Qu’est-ce que tu croyais ? - French example sentence - Tatoeba and it really seems that some of the translations are wrong as they use different tenses. The German translation is also present tense (“Woran denkst du?”), I would translate the German sentence into English as “What are you thinking about?”, which is also one of the translations on tatoeba.