If I were to attempt to assess this situation I'd wager Yaya's birthday has the sum total of fuck all to do with anything. This smacks of a player, and an "agent", recognising that Yaya has probably just had the season of his career, and that his value will never be higher, especially given he's now 31 years old. They are both aware that he's got 3 years left on his contract and, as such, he'll be 34 when that ends, and his ability to get another huge contract will have diminished. Whether this is he agent's idea/plan, of that of Yaya, is unclear, but it would seem someone has decided this is the time to rock the boat and either unsettle the club so he is sold (and gets a huge payoff, and huge new wage in the process) or force City's hand into offering him an improved contract of some description. My money would be on the agent (who, lets face it, won't be getting any big paydays anytime soon if he lets Yaya see out the rest of his deal at City) and Yaya is either happy to oblige or else is naive and can't see that his "friend" Dimitri is actually a leech trying to suck the last bit of revenue he can out of his charge.
I simply can't see City having treated Yaya in anything other than an exemplary manner, the behind the scenes picture you're given is of a happy, harmonious dressing room, and attentive and professional backroom staff, and a hands on, approachable directorship/chairman. Any slight Yaya may mention in his post World Cup statement (a timescale that does City no favours and allows this issue to fester and rumble on for the next 2 months) will be a perceived one as opposed to an actual one, and is more likely to be a smokescreen for what is really going on here, a moneygrab (either from us, or from another club eventually). City actually find themselves in a strong position here, Yaya has 3 years on his deal and, quite frankly, he's made himself look petty, childish and more than a little pathetic by getting his agent to cry on his behalf, especially about something as inconsequential as City apparently not celebrating his birthday with the right amount of gusto and reverence. One would think paying him almost £11m a year would be recognition enough.......