From the article, they may not be staff. Many research agencies have "fellow" or "associate" positions that aren't full time staff. Similar to a contractor but

From the article, they may not be staff. Many research agencies have "fellow" or "associate" positions that aren't full time staff. Similar to a contractor but used for postdoc, graduate students, etc. Sometimes on the path to FTE status, but not always. Could also be non-citizens on a visa for their term. Pay (think stipend, not salary) for these positions are more than what a grad student would get from their university, but not much more. At least from what I've seen (don't know details of NIH). For postdocs/grads/etc without families this can work, but cost of living in the DC area is high.