Talks about bodyweight are nonsense, strength gain is not linear, you dont' gain X kg on your max lifts for x kg of bodyweight gained.
Strongman deadlifts are also not comparable with Classic powerlifting deadlifts.
First Strongmen use a deadlift suit, which does not help much in this event, unlike in the squat or the bench press, but if they put the time to suit up, it's not for nothing.
However the straps are a game changer, they nullify the effect of the grip, which is problematic because a deadlift is, amongst others, supposed to measure of much you cand hold a weighted bar.
In Strongman, hitching is allowed, somebody mentionned, that Eddy Hall held the bar longer during his record. This is only partially true, he was hitching, because he struggled to lock out his knees (which would have had is attempt invalided)
There is also a difference with the bars that are used, Strongman deadlifts use a 'deadlift' bar while classic PLer use a 'stiff' bar. The latter is more difficult to handle.
All in all, Deadlift is the least strength/bodyweight related event in PL, this is the only event where lower weight class PLer can match SHW Pler.