The distinction between God-centered beliefs and Human-centered beliefs is one of faith in a supreme being or faith in the self.
Those who believe in God tend to believe that there is a goal or plan in place, and that their actions are simply part of this larger plan; they work, eat, marry, etc. all in the service of God's plan. This means that everything is centered on relation to God; an act is moral or immoral depending on how it will affect one's relationship with God and so every decision and action is centered around God. Therefore, the actions and reactions of everyday life is meaningful only in their spiritual consequences.
Those who do not believe in God, or who believe more in the self, tend to believe that their actions are uniquely significant based on relation to other humans (or, sometimes, just in relation to the self). This means that you make your own goals and purpose, and that you have the free will and ability to make your own destiny regardless of any higher power. This is not necessarily anti-theistic: many people think that their human lives are of paramount important outside of their religious beliefs.
To sum up, a God-centered belief system would tend to place importance on the Self only as it relates to God; a Human-centered belief system can coexist with religious beliefs but puts more importance on humanity as a whole and as individuals. (Opinions on the morality of each will depend on the personal beliefs of the opinion-maker.)
No. Not really.
Or rather, yes. It depends on how you take 'human-centred'. It is impossible to be God-centred and self-centred at the same time.
But, God does command us to love our enemies. In Matthew He gives us the summary of the law: "Love Me with your whole heart, soul and mind. This is the first and great commandment and the second is like it: love your neighbour as yourself."
In the 10 commandments, the first four refer to our service to God, and the last 6 to our service to our neighbour.
We are to respect God's love for us by passing it on to others.
So by loving our neighbour, we are being human-centred (if you want to twist those words). Otherwise, we cannot love God and ourself.