Well, my personal view is, I feel really sorry for your parents, who are probably worried sick about you, and furious to boot. If my daughters partner physically abused her and frightened her shitless, even once, my trust and respect for them would go out of the window, probably never to return.
Yes, I know its between you and your partner, but to your parents you will always be their 'little girl', who they will never stop worrying about and wanting to protect. I'm not sure an appology will make any difference to how your Dad feels. I think most parents (especially Dads) always struggle with their daughters partners somewhat, because lets face it who can live up to the ideal you want for your children? But your partner hasn't just slipped up in a slight way, he has slipped up BIG TIME.
I think its rather sweet (although old-fashined these days) that your Dad had that chat with your DP. He probably felt after that they had an understanding. You know, 'I am letting you know how much my daughter means to me' kind of thing.
I don't really see the point in you asking your DP to appologise, for two reasons. One, your DP has to mean it and if you got him to do it he obviously doesn't and Two, I don't think your Dad will feel its enough.
As a Parent, if my childs partner came up to me and said 'You know that chat we had, about how much you love your daughter and trust me to treat her properly? Well, I'm just here to say sorry for attacking her' I'd be hard pushed to find any forgivness in my heart. I don't know if I'm right in feeling that way, its not particulaly constructive I know, but thats how I would honestly feel.