KDKA is in Pittsburgh east of the Mississippi, begins with K.
KDKA was the first licensed commercial radio station. It got its license in 1920 and broadcast on 500 mightly AM watts. The “K” call signs for west of the Mississippi didn’t come into play until later.
Yes there are a handful of older stations in the east starting with K. I recall KYW in Philadelphia is another.
And a handful in the west start with W. Such as WACO radio in Waco, Texas. I think all such exceptions are very old radio stations which were assigned call letters before the current system was set up.
The Mississippi is rather dubious when it comes to Pittsburgh... or they just ran out of ideas...