When you tell someone they don't have to pay a tax that they otherwise would have to pay, the "welfare" is the amount of taxes they got out of paying. That's money in their pocket that otherwise would not be there.
Well, yes. I have money in my pocket that otherwise would not be there if there were a 100% income tax. Is that a "subsidy?" I guess the profits of oil companies are a form of "subsidy" from companies that buy oil, just like every business in existence is "subsidized" by the consumers who patronize it. The point is that it isn't a government subsidy, which is what "corporate welfare" typically refers to.