Depending on the aircraft type, and particularly Boeing v. Airbus, it could have neen any number of things. The first few moments after landing are pretty busy. It could have been a warning light indication concerning the thrust reversers, which require a "squat" switch to be fully compressed by weight on the wheels, to be fully armed for deployment. Or a momentary hydraulic pressure warning light. Or something as rare as a momentary extinguishment of the nose wheel down and locked light. But it was more likely, as a prior poster mentioned, a tower initiated go-around for some reason such as a runway incursion or a problem with a "hold short" instruction not being read back (confirmed).