Normally in TC of PTAT voltage is about 2-mV/K, which is same as TC of BJT (if BJT is used to contruct a bandgap circuit), so that these two component can be cancelled through out the intended temperature range.
The question wasn't well asked, the answer is totally wrong.
these are the comments, anyway, I try to contribute whatever i can, but in this case, i just have to tell the authors to not waste time posting nonsense