Yes, I have come upon split bus panels over the years. main reason for using these is ....there is no 'main' CB; via the six-switch rule. The top section is 'supposed' to be ONLY 5-2 pole breakers (the 6th feeds the lower section)
Now, the above being 'the rule'; I came upon many that had more then 6 switches in the top section.
That's the only reason that I can come up with for this setup.
