The bike does not have an ABS light, the gauge has a cutout for an ABS light when ABS is installed. Simple as that - and no, you don't brake any differently if you have ABS or not.
Yes, the light comes on in a car or on a bike whenever the vehicle is started. It is part of the start up process. It also comes on if there is a problem with the ABS system in either a car, or on a bike. Even if there IS a problem though, if it is the amber ABS indicator that lights up, the brakes default to a standard non-ABS system. The ABS system can completely fail, and the brakes will work normally.
Bottom line is, the guy had an accident, he functionally lost his wife, and is now trying to make someone else pay for it. While I have empathy for him, he is not only wrong, but he has a complete jackass for an attorney.