The differential amplifier inside the OpAmp have offset current and offset voltage which is said to cause an output error when there is no input.
This makes sense to me if the output of the differential amplifier is a differential one (double-ended output) in which each output is referenced to one another. So that if one side is higher than the other, it will cause an offset voltage at output.(so output is not zero anymore)
But I don't get why that also applies to diff amp inside the OpAmp that has a single-ended output. The output of singled-ended diff amp is referenced to ground so that if one side of diff amp is in offset compared to the other side it won't matter since I'm getting the output in only one side (I think)