I think he felt such a surge of pride watching his two girls that he got carried away with what he was saying. After all he no longer gets to read their report cards, watch them win as part of a sports team, see them take part in science fairs, music recitals, swimming races etc etc.
Here was something normal fathers experience all the time and he was just so proud of them watching them on stage.
I think his pride is just a result of how well their performance reflects on him as their parent, in a smug, showy-off way, rather than about what the kids have actually achieved.
He places so much importance on performing and putting on a show so no doubt he would've felt pleased to see them do well but his approval wouldn't have come from a place of love, nurturing and a 'healthy' pride.
If he was feeling proud of
them because he was seeing the culmination of their hard work paying off and their confidence and skills developing (and they may actually be very good as well, as a bonus)...then surely we'd see him encouraging them more with other things but instead they are sheltered and not given the opportunity to develop skills, broaden their horizons and grow.