I think that means including in pubs etc, not that a pub will be limited to 6 on the premises. As pretty much all pubs are just booking tables of 6, it won't change that much other than that if someone rings up and asks for "can I book two tables of 6" they will have to refuse, and if they find someone has done that independently and then interact they will have to ask them to leave in the way some campsites that are fussy about groups do.
Which is as I see it, so really it's pointless really, as you could have 20 to 40 'under one roof'