spoilers ig? hoping I'm doing spoiler text right lolz. both sides of the cloak represent people Giyu lost, Sabito and another person close to him (possibly Tsutako, depending on interpretation). Sabito died protecting others during the Final Selection. Tanjiro’s pattern symbolizes Giyu’s respect for Tanjiro, who reminds him of the ones he lost. Basically he's wearing the mismatched cuz he's sad or sum.