That the Donald wasn't a Christian, among other things.
Francis' comments were made in Mexico and regarded Trump's comments about building a wall to keep out immigrants. Francis said that true Christians build bridges not walls. Trump's response to it boiled down was this: It's not his fault he said that, it was those dirty lying Mexicans who had turned that nice old man into a political pawn. No Donald, he responded to an exact quote from you. But at least you are smart enough to not attack the Pope.
So, what does this mean? First it means that by extension if you support Trump's comments on immigration then you too are not a Christian, or a particularly good person. Second, it means that the world is watching, as it always is, and Francis' comments are reflective of that. Third, and perhaps most importantly, it likely sows us that anyone who supports Trump probably doesn't care what the Pope says anyway. I grew up in church where everyone was sure that the Anti-Christ (never mind that the word only appears in one tiny book - 2 John - and refers to all those who reject the incarnation) was either the Pope or a future Pope and anything said was a good enough reason to do the opposite.
He also said that contraceptives were OK to fight the Zika virus, which is one of the few exceptions in a doctrine that goes all the way back to the second century.
In his Border Mass he condemned both countries, in particular on the spiral of drug violence in the area. While advances have, seemingly, been made the reality is that much of that part of Mexico, and pockets on the US side as well, are controlled by the drug cartels. Who also profit from human trafficking.