Generally a footgun is something that's designed in such a way as to be extremely likely to be used in a way that's going to cause problems for yourself.
Yes it's a play on shooting yourself in the foot, the idea is that you designed a gun designed to shoot yourself in the foot.
It's talking about shooting yourself in the foot, but doesn't blame the victim. For me, it's one of the better cultural changes in software development in the last five years.
