If he had genuinely been afraid of assault he would have stood up as she approached, to make himself less vulnerable.
He was angry rather than afraid.
He doesn't exactly grab her by the throat, but you can see that he initially tries to get his hand to either her chest or her throat as he pins her to the pillar. Her arms are up to protect herself which is why he then seizes the back of her neck.
He uses his physical strength to overpower and intimidate her, and claims that it was because he himself felt vulnerable. Everything about the clip - from the black tie to the way he remains seated as she approaches before appearing to 'snap' - makes this seem extremely implausible.