It is in no way a requirement for slavery, if we look at it from a historical perspective. Any number of factors could make the foundation of slavery, including racism of course, but also nationalism or class-splitting with a hereditary power hierarchy like in some nations east of Europe. From vikings to Romans, slaves has had multiple colors throughout history.
Or necessary for slavery... Racism was a result, not a cause, of slavery, and not all societies that enslaved people of another race became pervaded with racism to the extent that the American South did. ~Thomas Sowell
Racism was the method by which slave owners tried to prevent rights being given to slaves.
It's been around ever since Europeans began their conquests to other countries and since then, they have used racism to justify horrible crimes (mass genocide, rape, slavery). They've enslaved Africans because they needed labor and since they deemed these Africans to be less intelligent/to have less morals/and to be less human than white people in general, they decided; 'why not use them instead?'. They perceived and treated them as everything except for human and this is because of their racist perspectives, they saw them that way BECAUSE they were black, which makes it racism. So whether the statement is trying to say racism in general or racism towards black people didn't occur until after slavery (its kind of unclear to me), they're both false statements, because no person would treat an entire minority as actual animals if they don't have some kind of prejudice views about them.
The had to feel better than blacks to enslave them, rape women, and kill hundreds. No way they didn't feel any superiority when they first came across blacks that had barely anything and didn't understand their language. But still they could've just went with it and decided to hit them again because they wanted power