I think RudyNate has it right. If he didn't want to talk to customers, he shouldn't be picking up his business line.
(Assuming he has a separate phone for business, or is able to see on his only phone whether the person calling is friend or client.)
Personally, I don't call anyone after 9 p.m. unless I know they are available to me at that hour. If I know they are not, I might only call if I need to leave a message for them to get that night or the next morning. So, to me, 9:00 p.m. is too late.