'Tis the season when if they had been near a male that they would be dropping litters. Maybe they are just in their prime and when they weren't fertilised they will need to dump the jellies, and they could both have geared up to breed twice. If it happens again this year I'd start wondering, I'd go with coincidence so far as I can't think of a natural driver which would develop the sort of feedback loop where one female prepares to get knocked up as another gives birth (or throws jellies), it could be that the environmental conditions have mimicked spring twice?