This generally occurs when a helicopter is taking off, landing or hovering with one skid/ wheel in contact with the surface. The helicopter may begin to roll about the point of contact with the surface (pivot point). The pivot point could be for example a skid/wheel, stuck or restrained to ground, ice, soft asphalt or mud. It could also be a skid/wheel contacting a fixed object/ground whilst hovering sideways or during slope operations.
That is the only mention of it in the first document and, whilst I agree about contact with the ground, I disagree about the fixed object - that is flying into something other than the ground and having an accident.
The second very good article doesn't mention it at all, it is a perfect treatise on dynamic rollover and explains the difference between static and dynamic rollover far better than the EHEST document.
And bear in mind that the EHEST document isn't a training manual it is to help operators to implement their SMS.
The main difference is that in dynamic rollover, adding collective makes things worse (unless you are lucky enough to break ground contact) - but if you drift sideways into a fence or wall or similar obstacle, adding collective will put you above it and remove the problem.
I'm not saying you can't end up in a smoking heap by drifting into something - plenty have done it - but it isn't what is referred to as dynamic rollover as illustrated by the US article.