That pun is so silly and childish that I can't see how could
anyone take it as a serious attack on abused children. It's a pun that RMS came up with, the same way as some child, unaware of PC culture and consequences of joking about no-no topics in the modern world, would make it.
If you assume bad intentions, everyone in the world will have made a faux pas that can be perceived as offensive. I do not assume bad intentions in RMS's case - he has done so much good for the world, and such a person obviously cares about humans, including abused children. The fact that he made a pun about abused children doesn't bring harm to anyone.
If you asked him for serious thoughts on the topic of abused children, you would most likely receive a completely different response, one that you would probably like.