‘Very odd, though, that they should describe a system they admit to be based on the exploitation of wage-labour as some kind of feudalism rather than of capitalism.’
A non-marxian use of ‘wage-labour’ is all that is, if that is indeed the term they used.
Those (including self-intentifying marxists) who advance the view that the myriad leninist state at one point in time or another were not capitalist (in the *marxian* sense) but some other system of undesirable,un-progressive/regressive exploitation will use such terms as ‘wage-labor’ and even ‘capital’ (when they should properly say ‘means of production’ for the latter) as a kind of set of default/analogous terms.
(As for anarchists, Kropotkin, unlike many other classical anarchists, did not believe in the marxian labor theory of value at all yet he used the terms ‘wage-labor’, ‘capitalism’ etc. Nothing strange in that.)