Yemen isn't in Africa. I doubt many African countries where China has an interest care about Yemen.
Here is an interesting article about Africa's relative non-importance in Chinese foreign policy circles. If there is a sub in the mix, it's likely because the military wanted to do an exercise, not some sort of mischief-making at work. That would require a much higher level of attention than Africa usually gets.
http://www.brookings.edu/research/pa...ign-policy-sun
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