I doubt you would believe you were actually going to play very much going forward if your boss had told you that you were worth a mere 25% of what you were the previous season.
Very obviously, because he didn't move on to another club, giving up football at that stage of his career wasn't much a of a wrench for him. If you were in the twilight of your career and your boss told you he didn't think you were worth the money any more, and you said "Ok boss, I'll take a pay cut then" and he came back with "I reckon you're worth maybe 25% of what you were last season", I doubt you would have this burning desire to keep working for him that you seem to think Numan should have felt either.
Football players aren't 10 year-old boys in awe of their boyhood club. They are professionals who are as entitled as any other professionals to tell their employer to take a hike if they try to take the piss. Numan seems like a good bloke, loves the club, has time for the fans and, judging by the way his career ended, he knows his own worth too, as everyone should.