The suit alleges that the Giants interviewed Flores simply to satisfy the NFL's Rooney Rule mandate requiring that teams interview minority candidates.
I'm not an attorney but it seems that neither of these is the basis for a lawsuit.
OTOH, Flores just guaranteed he will never be hired again in the NFL. Plenty of other black head coaches have been fired - Romeo Crennel, Anthony Lynn, Ray Rhodes, Mike Singletary to name a few - and no one ever brought a lawsuit.
I would further add that as the head coach, you work for the owner and the owner alone. He can fire you at any time and for any reason - even if he just doesn’t like your socks. Jerry Jones fired Jimmy Johnson after he won two Super Bowls.