He may have thought so because the phrase "income inequality" is usually used in the context of describing it negatively (in the US at least). I guarantee you that the phrase "income inequality" is used by Democrats in the Senate/House 10x as much as Republicans. No Republican is ever going to say their tax cuts for the wealthy "increase income inequality", they'll say it "helps the job creators create jobs".

Edits: Wow, I need to learn to make sure I reread sentences in full when I go back and reword something.