On one hand, Tonbokiri is glad that Izuminokami didn't take that as a slight against his pride as a sword.
On the other hand, he'd not expected such an amusing reaction! He's embarrassed over that? (To be fair though, he doesn't have much room to talk himself.)

"Of course. Of course." Tonbokiri gives Izuminokami a sound, reassuring pat on the shoulder. "In apology, I'll get you an apple as a treat when we go back inside. They're very delicious right now." (Is he still teasing? Maybe just a little.)

Mikuniguro knows that key word, and wants an apple too! Hey! He shoves his nose into Izuminokami's side.