It suggests larger helmets incur higher levels of rotational acceleration compared to medium sized helmets. It could be an issue worth further investigation. I would be concerned at wearing any large helmet.
ps
Unhelmeted 7.5 to 12k, J size 10 to 20k, who knows what M or O size would result in.Assuming that the response of the unhelmeted head is similar to the helmeted head during an oblique impact at 8.5m/s at 15º, this may generate between 7500rad/s² and 12000rad/s² of rotational acceleration. This is potentially more severe than the 3000rad/s² to 8500rad/s² measured during abrasive and projection oblique tests with size 54cm (E) helmeted headforms. However, for the most severe cases using a size 57cm (J) headform, rotational acceleration was typically greater than 10,000rad/s² and increased to levels of 20,000rad/s², a level at which a 35% - 50% risk of serious AIS3+ injuries is anticipated.