This statement is true in its literal sense but very misleading. Holding currency is close to a zero sum game, holding wealth is nowhere near that.
If someone were to, say, sell me a pound of gold for $1, he would win in terms of pure currency. He would have one more dollar, and I would have one less, but I think I would come out ahead.
Similarly, if someone sold me a tool I needed to do my job, he would clearly win in terms of money in that transaction, but I could turn around and use that tool to create new things that never existed before and create more value in the world.
Paul Graham talks about this in more detail and more eloquently than I can hope to at http://www.paulgraham.com/wealth.html
(Edited to add a small comment).