Deku saying Dabi is not Endeavour is similar to when he told Shoto his power was his own but the intention isn't the same. Dabi places the blame of his crimes on Endeavour. He repeatedly says his flames are Endeavour's, even burning Nejire and immediately saying it's Enji's fault
Deku isn't trying to reach out to Dabi, but calling him out on blaming his father and denying responsibility for his own actions, while acknowledging that Endeavour is responsible for Dabi's trauma, but not for his crimes.