Since global warming is a global problem (and other forms of pollution from burning coal or gas can travel long distances) it doesn't matter where the carbon is saved, it's basically equivalent, so they're just being pragmatic in their philanthropy.
This could be thought of as a subset of their wider goal to be carbon neutral (which again, could be described as philanthropic in nature), presumably funding the roll out of renewable energy seemed like a cost effective way to work towards that goal.