Earlier quoted context omitted.
How can that claim be made?
By carefully reading their statement and to realize that they have very explicitly not said that they are assuming responsibility for these figures in their role as CAs but that this is merely Binance's opinion expressed on Mazar's letterhead.
This alone is at least a gray area, ethically, and not necessarily in just this case.
In this particular case, it has made it possible for Binance’s chief strategy officer, Patrick Hillmann, to say things which he subsequently described as “parroting others’ descriptions of this as an independent audit.” Mazar's response so far: "No comment."