I suppose the question would be whether that atrium area under the veranda is classed as private property. If it is, then once the landowner or their agents have made it clear that they (as in anyone, not just protestors) don't have permission to be there, then there is an entitlement to use reasonable force to remove people from the land - so a claim of "assault" is somewhat overblowing it, though it's never nice to be physically moved or shifted.
From the very short clip of the staff getting hands-on with the protestors, it certainly didn't look unreasonable in terms of force, but then I think calling that a private place where there's no prevention of access to that area for the wandering general public would be a very difficult position to defend.
Still - it's noisy, it got publicity, and I'm reading about it now - so the protest worked. Good on them.