It does make you wonder if he was just warming up or wanted to taste what Brook could counter with knowing he couldn't be hurt, but that would be a bit bonkers to any other fighter though. Or maybe it is to make himself look a bit more vulnerable and encourage any onlookers. Either way it was strange as he didn't even need to throw those punches as he surely knew himself they were not landing. It somewhat helped Brook look quite good, but it was really GGG just saying 'That's as clumsy as I can be and you don't really have anything'.