Surprisingly, as so often since documentation in Matlab is example- instead of syntax- driven, the actual rule one looks for isn't described... :( (I've complained of this for 20+ yr...it's improved with more examples and some amplifications, but still has ways to go...)
Anyway, rant aside
S=string(C);
is the example not given of an array; I'd surely expect it to work.
S=string(cellstr(C)); % is in the example if above doesn't
Don't have recent release with strings class here so can't test...
