How is This a True Statement?

[MissionStanford]

"If two compounds have the same relative configuration and you know the absolute configuration of either one of them, you can determine the absolute configuration of the other."

Elsewhere in my book it seems to contradict this. It says:
"Two compounds with the same relative configuration do not necessarily have the same absolute configuration."

Which (Unless I'm reading this wrong) would imply that even if you know both compounds have the same relative configuration and know one's absolute configuration, the other one's absolute configuration may or may not be the same, so you can't determine the absolute configuration of the other.

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[gettheleadout]

If the two compounds are stereoisomers then relative configuration would mean this: http://www.acdlabs.com/iupac/nomenclature/93/r93_635.htm

And thus you can figure out from one's absolute configuration what the other's is.

If they are totally different compounds, relative configuration may be referring to D- and L- isomerism, which does not correlate with either R/S configuration or (+)/(-) optical rotation.

The term relative configuration seems to be vaguely used and I don't remember encountering it in organic.