I have just seen this, so probably irrelevant to post about it now but I would like to point out a few things.
Mallorquin is a variant from Catalan, the main differences are the pronouns, and a few words, other than that is Catalan (actually, most Mallorcans would say they speak Catalan, although there is a very vocal very nationalistic segment in society who claim mallorquin is a language in itself). And no, if the only difference you have appreciated is Gracies they were speaking to you in Castellano!
Don't forget that most adults were brought up in the last years of Franco dicatatorship which means they speak Spanish (castellano ) perfectly but some resent to be forced to speak other language than their own (no surprise about it to be honest particularly when they were punished for speaking it in times gone by).
The only thing that I think would be confusing about learning Spanish in one of the "Catalan Countries" is the speed at which languages are changed during the conversation: When two persons meet for the first time, the language they speak on that ocassion is set as the language to speak when meeting again, which means that you can have a table with 3 persons where every person is using both languages when adressing the other two.
Ahhh, and as everybody speaks both languages, and they switch between them so easily, they are prone to forget that someone in the group may not be able to understand one or any of them. And to be honest... I don't blame them!