Carrier frequency offset and carrier leakage
I think you are confusing two different things.


Carrier offset is the difference between the transmitter's and the receiver's local oscillator (LO). The receiver needs to eliminate or reduce the offset if it hopes to receive data consistently. This is done by estimating the offset and adjusting the frequency of the LO.
Carrier leakage causes a DC offset in the receiver. Consider the receiver mixer: it has two inputs, one is the received signal, and the other is the local oscillator. In practice, the LO signal will be present at both inputs, because it is very difficult to isolate high-frequency signals in a PCB. This causes the LO to mix with itself, producing a DC term at the mixer's output.