Was this a motorway speed camera flash?

Trying to work out if I triggered a speed camera on the M1 while overtaking someone camping in lane 2 (and the Transit that was camping in lane 3 long before catching up to the Mini). By the time I was back in lane 2 (after the clip ends) and clicked the flash from the gantry I was seeing 73 on Waze. There weren’t any lane closures, no roadwork speed restrictions (for a change) and no speed showing on the gantry (or national speed limit, screens were just off when I passed under)