You don’t have to assume altruism here. The big difference between the west and China is that the west has lots of military presence in Africa while China does not. When countries refuse to work with the west on western terms then the west will either do a regime change, destabilize the country, or outright invade it as happened with Libya. The relationship between the west and the countries it subjugates is inherently coercive.

On the other hand, China does not have a history of using violence against countries that don’t trade with China and it does not have the military presence to threaten the kind of violence the west has been using when it doesn’t get its way.