He is referring to is the finite supply. In 1960 the entire US monetary supply (M2) was $300 billion. Today it's $22 trillion. When there's so much more money out there inflation is inevitable. Monetary velocity is the true driver, but greater supply tends to drive greater velocity.

By contrast sometime around 2140 the final Bitcoin will be mined, and we're already reducing the number mined per block. Inflation can still happen for reasons besides supply, but it's generally much less probable.