“Fulānun kathīru r-ramād” leads from plentiful ashes, to extensive cooking for guests, to generosity. It is a classic allusion to a quality. The literal meaning remains possible, even though the intended sense is generosity.
“Al-karamu taḥta ridāʾih” places generosity beneath a person's cloak to attribute the quality to him indirectly: an allusion concerning attribution. Both use indirect indication, but the rhetorical target differs.