Absent any laws addressing operating a firearm under the influence of alcohol (stupid, but not illegal) the police had no authority to do what they did for the reasons stated. Also, it reads like the cops had the opinion that he drinks too much. Do they have any evidence of it? DUIs (for a blind guy that would be some pretty incriminating evidence)? Drunk in public? They have no authority to do a blood alcohol test under the circumstances stated in the article.
Let him keep his guns.