I think it's just an errata of sorts. Berserk Charge is obviously meant to affect blood claw models, not the attached wolf guard model. At least that is what makes sense to me, the seasoned veteran shouldn't have Berserk Charge.
Although I do wonder if we'll see a mechanic to 'add' a primaris WG model to a unit. They seem to have implemented a mechanic like this for the Deathwatch, so I don't think it is infeasible.
Edited by WrathOfTheLion, 18 October 2020 - 01:28 PM.