I have seen many reactions in fish from the mirror... Some investigate it, not scared at all... Another decided to attack the mirror repeatedly with his little mouth, some tail slap it, some circle it flaring, and others back away.
As for the female, take a look at the picture I have attached. This is Janey.. Once a pale little thing, now looks like she has been painted blue! Since breeding her (twice now) her color has enhanced and her caudal has gotten longer and fuller. It's a way of saying "I'm ready, and I'm viable to breed with you". The vertical stripes are submission stripes. I rarely get to see this anymore as I have mainly light girls but I have a few plakats who are darker that may be bred. That with the heads down slow and intent dance she was doing... Is saying "I submit fully to you".
He may have a different reaction seeing a male (the mirror) and seeing a female, as you noticed when he backed down to the mirror, but came out eventually to the female. He's a lover, not a fighter ;)
And contrare to popular belief, males don't right out attack each other (at least most of the time). They tend to put on a show... Circle each other, flare, chase, tail slap, stare down, etc, before actually harming each other. Though this is not true in some cases, most cases it is. It's a "I'm prettier than you, bigger than you, better than you."