“/r/ voiced alveolar-dental flap; it occurs in word medial positions; it does not occur in word initial or final positions.” —A Grammatical Sketch of Isaalo (Western Sisaala), 2006, p. 57.
They’re just changing ɝ or ɚ into something closer to ɛ - if you asked them to actually say “Weck”, it might sound different. But you can hunt all you like to find the actual “r” in an ɝ sound - there isn’t one. What I mean is that you’re not saying an “r” in “work” any more than the Africans are. (Unless you’re Scottish or something.)