Layer feed is bad for roosters and cockerels long term. It harms their kidneys. Plus, some All flock does not hurt the entire flock as long as they have oyster shells. Grower/All flock feeds also tend to have higher protein. 18% is usually the minimum for chickens.Many people use layer feed for flocks with roosters, myself included. It looks like your potential rooster turned out to not be a rooster, so you won't need to worry about this for now, but something to keep in mind for the future!
No need to immediately discount layer feed with a rooster. There seems to be a chance that some roosters on layer feed will have a shorter lifespan from excess calcium being hard on the kidneys, but honestly most roosters don't live out their full life span anyway. If predators don't get them then you've got humans turning them into dinner if they get aggressive or selling because they are starting to inbreed.