Did Decred developers, or did the community pay for the listing fees? I heard that Binance makes a lot of profit from it because they are very expensive.
No one paid.
CZ tweeted that it was for our strong community

I really wonder how many decred he bought before this announcement.
yup. they've must have earned a huge profit from trading and selling their own part of coins. exchagne like a binance won't list any token for free . but if it does they'll see a huge profit in it. without that they won't do it.
anyway. they did it for free but it is a very huge thing for Decred also to get listed on Binance for Free.