The explanation was reasonable. It reduced his frustration for why they were asking for energy stones. But being reasonable doesn't change the fact that he doesn't have energy stones. Without energy stones, he wouldn't be able to purchase the non-human races.
He wasn't content that he wouldn't be able to use dollars to purchase the non-human slaves, so he asked, "Human slaves can be bought with dollars. Why can't they use dollars for the others?"
His question made Wrath laugh. She said, "Our currency is useless. The dollar is useless. There are a lot of things that are used as currency in the universe, but the dollar is not considered a currency at all. It is because it has no value."
"Before you argue, consider that the dollar is produced by someone. In its physical form, someone is literally printing it somewhere. How can such a currency be taken seriously when someone can literally print it and offer it to you to get something you worked hard for?"