Been seeing a lot of people misread this scene. Eren doesn’t tell Mikasa sorry, Historia does, because Mikasa was addressing her when she brought up Eren’s training.
Mikasa: “Give it to me” (speaking to Eren)
Eren: “Ah, Hey!” (speaking to Mikasa)
Mikasa: “Eren is tired from training” (now Mikasa is addressing Historia)
Historia: “You’re right….sorry Mikasa”
The two girls begin to walk away, prompting Eren to go after them yelling “Don’t treat me like an old man!”
Just to clear things up.