Are you sure it was man-to-man? It's not always easy to tell, especially around the puck where a defender is often "taking a man" even in zone defenses. A lot of teams also use a rotating zone coverage down low (between the two defenseman and the center) that often visually looks like man-to-man, especially when defending a cycle. It's also not easy to tell on very short possessions in the zone where the offense and defense never really have a chance to get "set up."
I didn't watch every second of the game, but I didn't see any of the distinct visuals (mirrored motion across the entire ice, etc.) that suggests a full man-to-man to me. Guys down low weren't sticking with their man outside of their usual zones of coverage (i.e. defenders/centers weren't following guys around all over the zone), something that was very noticeable previously, and the forwards up high (especially on the weak side) were often collapsing extremely low regardless of what was happening at the points, which is something they wouldn't be doing in a man defense. The emphasis in general away from the puck seemed to be pretty heavily on controlling space, not manning up tight.
It looked like a form of the low-zone collapse or sagging zone in the windows of play that I caught, but maybe someone else saw something different.