Other executions by beheading were bungled, but this one wasn’t- it was a single clean cut, which suggests an experienced headsman.
Nobody actually knows who swung the axe. The official executioner in London at the time was a man named Richard Brandon, who denied having done it until his own (natural) death six months later. There were various other men rumoured to have been the executioner, one of whom stood trial for it after the Restoration and was sentenced to death, but then had the conviction overturned when he was able to prove it wasn’t him.
The executioner, whoever he was, wore a mask (which wasn’t normal practice, cartoons notwithstanding) and did not, as was customary, announce “Behold the head of a traitor!” as he held up the king’s head- possibly for fear of being recognised by his voice.
