The arrivals in 1619 were not sold as “slaves” but as indentured servants which was slavery for a usually 7 year period and could be extended if the servant ran away or was caught up was caught up in some other infraction but it was not officially slavery.
We didn’t have slavery laws, so you couldn’t have “official slavery”. They used their process for indentured servants.
But as the participants were not willing, nor had they consented, or entered contracts, nor were they criminals, their servanthood was in fact slavery.
Slavery does not have to be a permanent thing to be slavery; that someone freed their slaves after a period of time does not make them less slaves.