My randomized seating chart ended up with all black students at the same group table

I teach a college level class for 11th graders. Each desk has a bio of a US president, and I call the president's name from a random bucket of labeled popsicle sticks for our warm-up questions. Because of the warm-up system, I enforce a seating chart even though my students don't really need one.

I make the seating chart by randomization the president names in excel next to a list of student names. I don't walk around and check who is sat where. When all students have been called randomly to answer warm-up questions, I randomize the seats again and post it on the wall (every 2 months or so).

Unfortunately, this time for one of my classes, every black student was randomly placed at the same group table. There are four black students and 5 seats in that group. I didn't realize it until they'd already been seated, and I left it the way it was because I did not want to draw attention to it. However, I'm worried the students may assume the worst. Should I do something to diversify the seating arrangement?