By explicitly not selecting for voting behavior for any party during the drawing of the districts, but basing the borders of the districts purely on a geographic or statistical property such as area and/or population. As soon as you start taking voting behavior into account you will be favoring either one or the other party.
That's an excellent question, which makes me wonder the Republican Party was not satisfied disenfranchising Democrats and catching Blacks as collateral dammage, but insisted on disenfranchising Blacks specifically.
For starters, the GOP could instead try and figure out why black Americans vote overwhelmingly in favor of Democrat and update their policy stances to reflect that. Instead, they're deciding to draw districts to lump them together so they can disenfranchise them and make their vote worth less.
So you're right there are racial implications, and it's certainly on the side of the GOP.