I think he is probably talking about how hard other elites/sub-elites run their workouts. Remember that in their staple threshold sessions (5x6 mins, 10x1km etc), the Ingebrigtsen's always focus on staying at or below their threshold (which is close to their half-marathon pace). Although they do a lot of volume, the majority of the Ingebrigtsen's workouts just aren't that difficult individually (obviously discounting things like the recent 6x800m workout that was publicised) .
In contrast, its easy to find other elites/sub-elites pushing their workouts constantly - just look on youtube. I remember seeing videos of Ed Cheserek always going way faster than his prescribed paces on workouts. Another example is this Paul Chelimo workout, where they push the pace much faster than prescribed.
Or that "alpha" dude from Ole Miss who would be vomiting after workouts, and so on and so on. The Ingebrigtsen's just don't do workouts with this intensity on a regular basis, because their approach is volume-based, with higher intensities only coming around race period. It's a lot more boring, but it gets them results. As someone else posted, it does seem like go quite slow (relatively) on easy days. Marius Bakken says that those following the Norwegian approach stay below 70% max HR on easy runs.