so. here is the thing. that. to me. is more of an indication the two hemispheres are independent and thus the left right thing. If we take the previous paragrpah into consideration:

There is also data pertaining to how hemispherectomy affects the body in other ways. After surgery, the remaining cerebral hemisphere is often able to take over some cognitive, sensory and motor functions. The degree to which the remaining hemisphere takes on this additional workload often depends on several factors, including the underlying etiology, which hemisphere is removed and the age at which the surgery occurs.[13]

In terms of postoperative motor function, some patients may have improvement or no change of their weaker extremity,[11] and many can walk independently.[13] Most patients postoperatively have minimal to no behavioral problems, satisfactory language skills, good reading capability,[13] and only a minority of patients have a decline in IQ.[14] Predictors of poor outcome may include seizure recurrence and structural abnormalities in the intact hemisphere.[13]

We can see that indeed the other hemisphere has to expand its capability from what it had pre surgery and that much of what they are looking at is basic function and not like if they were as good at art or reasoning after surgery.