Why did my local channels work before I paired my cablecard?

I installed my Bolt+ and had an inconsequential but interesting discovery. I took the cablecard out of my Premiere, installed it in the Bolt, and booted it up. ABC, CBS, NBC, FOX, CW, and PBS all tuned and functioned normally. Any other channel brought up that black and gray screen telling the user to call their cable company. I did not expect this.