The way I read it, 44 USC 3506(d)(4) (a) and (b) does not allow the government, once they have information they have disseminated, to restrict the public from disseminating that information, by establishing an exclusive distribution arrangement.

FBO.gov was the place where the government published certain information, not identified in any way as classified, restricted or otherwise unavailable to the public. Once they did this, they are not allowed by this law to interfere with public dissemination by creating an exclusive arrangement (ie only government controlled websites may distribute the data). Nor (4(b)) can they stop the public from redistributing that information.

Anyone who might have reposted information published by the government is allowed to do so and the government can't collect royalties (ie no copyright). In the old days, (pre-web) it would have been published in the Federal Register or the Commerce Business Daily, which can be freely copied and disseminated. The Web just makes it easier and faster.