The center of the question is the interpretation of the phrase "engage with." The statement is valid when speaking of the central theme of Existential literature, of which Absurdism is one manifestation. Ionesco, using a “social” mise-en-scene (in that the population is all becoming alike and non-humane – compare/contrast Gregor Samsa in Kafka’s Metamorphosis) to dramatize the existential idea that humanity is not “designed” but designs itself with every individual action, utilizes Absurdist techniques to move away from the social dramas that try to deal with real social problems. In other words, Ionesco’s point is not social – only his theatrical device. Compare his Exit the King, which, while superficially a historical chronicle play, is really about the question of whether humanity has an obligation to its own past. Ionesco, in all his work, does not "engage with" social problems, but uses them as a mise-en-scene to get at the larger philosophical question, a sort of metaphor for his existential dilemma.
Well, the main point is that Ionesco is not interested the the social-cultural world of the 20th century--he does not spend his creative energies dramatising social dilemmas, but in finding stage/dramatic physical metaphors for the dilemma of man's raison d'etre-- what are we to do with the fact of our existence? You can see how difficult this abstract idea is to articulate, but the stage is a good language to use, because it is "imitation in the form of action". When everyone else seems to conform, the one who doesn't appears freakish--there are all kinds of social parallels (bikers, Goths, tatoo freaks, etc.), but Ionesco is saying something more: what if Mankind itself is the misfit, the creature living a false life, following arbitrary rules that have no authority?
Can you please elaborate it a bit more?