THE EARTH A SPHERE. -- That the earth, too, is round is shown thus. The signs and stars do not rise and set the same for all men everywhere but rise and set sooner for those in the east than for those in the west;
So, a "sphere earth" describes the shape of the earth, as a whole (i.e. land + oceans), as looking at it from above, as one looks at a map.
Typically, "flat earth" is ONLY describing that the land mass is flat, from a horizontal view. Since 99% of flat-earthers aren't Trads, they wouldn't refer to the "sphere earth" idea.
Conclusion: These 2 descriptions aren't mutually exclusive, as they talk about 2 different things. The former concerns itself with the entire globe; the latter concerns itself with simply the land.