All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
It is known that owning slaves was common in that age, and it is not unlikely that ‘Umar had slaves like others who lived in that time. We advise against asking this kind of questions, which are of no real benefit.
Allah knows best.