This phenomenon is quintessentially mutual and void of strategic action and time ordering of events beyond the fact that both of your past relationships ended around the same time. Put bluntly, you both become single and then bam, one night you just start to hook up.
Person 2: Ya that's kinda weird. They both just broke up with their ex's a couple weeks ago
Person 1: I think we're witnessing the MRS phenomenon
Person 2: Huh?
Person 1: Mutual-rebound-sex