How does ʿaqartu maṭiyyatī differ from ʿaqarta baʿīrī here?

Imruʾ al-Qays: Dialogue in ʿUnayzah’s Litter, Boasting, and an Oath (Verses 13–18)

• Both mean only selling a horse
• Both mean sewing a litter
• The first is an oath, the second a prayer
• The first refers to slaughter; the second complains of harm from overloading