Let's turn this into something productive with our limited knowledge of this event.
I'm trying to, AF! I'm not casting aspersions, but I really do want to know what occurred here.
From my own experience (ahem) and talking to other owners, the cowling coming open has minimal effect on performance and handling (disregarding the startle factor). Depending on the cowling fit (they're all subtly different), if both latches are unfastened the cowl might open quite early, merely with the application of take-off power - obviously not in this case. However, should the cowl detach in flight then there's a chance that it might inflict engine damage as it departs. I don't think this is the case here though as seemingly it requires great speed - in 1959 the RAC of WA's VH-RFW lost its port cowl during a "very fast" spiral dive (one latch undone, the other then failed under the loads) and as the panel separated it destroyed the throttle linkage. Oddly enough, the Chipmunk crashed just a few miles north of Jandakot.
The latches are "fiddly" and, despite the presence of appropriate holes in the port cowling these sometimes don't line up (I did say that they're all subtly different), sometimes it's necessary to open the cowls to prime the engine.