Indeed, it is. The notion of bringing back slavery is about as absurd as the notion of bringing back feudalism.
Obama’s election proved that a lot of whites had moved past race and voted for a (half) black for president; Obama’s actions since then have proven the he and many other blacks have not. It doesn’t bode well for him.
There is a feeling of inferiority in may blacks that is just below the surface. Or maybe it is a feeling that they are often judged to be inferior by people that don't give them a fair chance. Either way, it is close to the surface and they are very sensitive to veiled references to slavery. And there is absolutely no doubt that Biden was trying to take them there.
Back during the 2000 election my stepson was teaching in a mostly black high school in Chattanooga. He actually heard black teachers telling students that Bush literally wanted to bring back slavery and some of the students actually believed it.
My stepson complained to the administration and they did warn the teachers not to do it anymore but the teachers eventually ran my stepson out, by making him miserable, and I'm sure they are still filling the kids heads with how evil republicans are.