Izuku sneaks out of the dorms at 4 am for training with All Might, normally without people knowing, just so that he can avoid suspicion. Aizawa gets off of patrol every day at 3 am, normally getting back to the dorms around 3:30. Izuku spent years taking care of his mom after long shifts at the hospital. Seeing Aizawa come back so tired really just woke that old instinct back up. Besides, he was making breakfast anyway, did it really hurt to make a little more?