Yes, many people think that but that's not how chicken terminology works. A chicken is only an adult when they reach one year of age.
Rooster - An adult male chicken that is over one year of age.
Hen - An adult female chicken that is over one year of age.
Cockerel - An immature male chicken...
I am sorry for your loss! I don't know what may have done that. It is sad that Polish have been bred to not see very well due to the large crest, and Polish have been known to attract hawks to your backyard. A hawk knows which birds are more vulnerable than the rest.
If he's only eight month sold, he is not a rooster, he is a cockerel. Give your cockerel time to get more hormones and see what happens-he may grow into a rooster who doesn't breed regularly, or he may not.
How old is the rooster? I have found that older roosters tend to not want to breed much. Also, a rooster knows when a female is not laying and he is much less likely to mate them then because there's no purpose.
Polish are a really strange-acting breed and are enjoyable to have because of their weird personality, but they do not do good at all in a mixed-breed flock. If you are getting a Polish, it is better to at least get another one so the Polish is not alone and is the only one who can't see well...