brejcha

well I was driving around today and my brake seemed like it got looser. I pulled over and popped the hood. I went and looked inside the brake fluid holder and the cap was a little loose. The brake light was on before I checked it. The fluid levels looked fine. I tightened the cap and when is started the car the brake light went off. The brakes seem tight again.

Is this something to be concerned about, or was it just the cap?