They probably forgot to mention because all Fuji X-series mirrorless cameras are APS-C. There is also a rumor that Fuji will release medium format mirrorless cameras soon...
Medium format is very relative. The size of the captor is probably going to be 4x5 like the new Hasselblad, which is far from a real medium format like 6x7... And it's going to be mighty expensive too, the SONY sensor used in Hasselblad is said to cost 4K USD alone.