Wasn't he reading someone else's quote?
Yes, he was. He was condemning the person he was quoting. By quoting them, he was entering their words in the Congressional record.
As for Biden's past voting record, I'm not surprised.
He voted against bussing students to schools far from their homes in the 1970s. It was a very controversial topic at the time and voting against it did not mean that person was racist or was actually in favor of segregation, just that they did not think it was appropriate to bus young children long distances as a means to remedy segregation and further integration.
The closest equivalent today to the bussing issue might be direct payments to descendants of slaves in reparation for slavery. Voting against direct reparation would not mean that someone was in favor of slavery, just that they did not think that would be the best way to remedy the lasting effects of slavery and that the money might be better spent another way.
Be wary of attacks like this from right wing authoritarians that take things out of context, alter videos, and otherwise manipulate reality for propaganda purposes in order to gain or maintain power. The fact that they are having to dig up things from 40+ years ago and take them out of context and lie about them should be a clue that they don't have anything better to attack Biden with.
Also contrast it with Trump's long and well-documented history of illegal housing discrimination, racism, etc.