It's hardly unbelievable, it's what most people would do in his situation.
Say you've managed to stick away enough cash to retire early, you still like what you do but you decide to jack it in and have some time to yourself, would you jump back into work for any job that was offered? Or would you be picky, only want something that was going to be enjoyable and convenient?
Curbishley can easily afford to sit at home doing $#@! all, aside from the odd bit of media work, he might still love the game but it's not like he's desperately throwing job applications around trying to get back involved is it? But if something turned up on his doorstep looking like a good opportunity then no doubt he'd reconsider his quasi-retirement.