My guess is they are Barred Rock, straight run, and the TSC employee was completely mistaken on what they actually have.
I have seen feed store personnel (including owners of feed stores) look me squarely in the eye and completely mislabel chicks. I once had the owner of a feed store flatly proclaim that you can't sex sexlinks...they come straight run.
So, while it is possible they ordered straight run Black Sexlinks, I find it doubtful as the store would get stuck with all the males since all the (educated) public would pull the all black females leaving the store with a bin full of males (not a high commodity). Stores can't make profits that way, so what you have in my opinion is Barred Rocks, straight run, and the employee felt he/she could distinguish the males from females using the Barred Rock patterns of female...small head dot, black wash down legs; male....diffuse head dot, no black wash down legs. (BTW, that coloring trick only works in carefully controlled BR lines and only within a single line).
My guess.
LofMc
EDITED TO ADD: The other option is that it is a bin full of Production Blacks, aka California Greys. They are similar to the Barred Rock and come straight run but are a hybrid like the BSL only there is no sex linking. A Cal Grey is generally a mixture of Barred Rock rooster over a Leghorn or Leghorn/White Rock mix....great layers of white eggs (unlike the BR and BSL which lay brown eggs).