Academic citations

ResearchGate, one of those citations services that have been popping up recently, sends me email to inform that an old paper of mine has been cited. Out of curiosity I looked at the citing paper. It is completely unrelated to the topic of my paper, which was not used in any meaningful way. The citation doesn't give a clue as to why my paper was cited, and the context in which it appears is not related either to the cited or to the citing paper. I know there is an academic citation industry but I can't quite make sense of this.