"Data are in current U.S. dollars." Plus, the growth has been large enough to outpace inflation except for the last couple years.
The percent of GDP has been dropping but that is just that GDP has been growing faster. Which means that the US has been doing more valuable things than making stuff.
Paul Krugman made this point in a podcast with Ezra Klein. People remember a time when manufacturing was 30% of the economy, but that will never return, because the economy grew far more than our appetites for stuff. His estimate was that even if it worked and jobs returned, you'd be talking about going from 10% of GDP to 12 or 13%.
The percent of GDP has been dropping but that is just that GDP has been growing faster. Which means that the US has been doing more valuable things than making stuff.