At that moment Tanjiro is reminded of and apologized to the two of them (Urokodaki and Haganezuka);
for Haganezuka, it's obviously due to the broken blade, but for Urokodaki, KnA jokingly states it's for Tanjiro accidentally seeing his true face when he's sleeping
I know the fandom has been referring the author as a she, but there weren't any photo or confirmation (that I can find) so I'm leaving out the pronouns. The leftover "he" was a mistake because the message was copy pasted from Ryōji Hirano's.
There's a lot of cases where the fandom made assumptions on the author genders that turned out to be wrong so I'm just being cautious.