I see some are confused so I'm going to offer my interpretation on the last scene.
When the prince stained Feria's dress and said to accompany him, it was his own strategy to try and ruin Feria, not in bad faith but to measure her ability since his little sister is taken by her.
If Feria had accepted to follow him her reputation would have took a hit since she would have been alone with him and accepted clothes from another man despite being a consort candidate.
Instead she made it so that both were in the same standing by having dirty clothes, but framed it as "since we are now in the same circumstance you don't need to offer an apology (by getting me a new dress, which would be indecent since I'm not going to wear clothes offered by a man other than the king)"
The 11th consort wanted to use this as an opportunity to discredit Feria and networking with the other country so she send her dad to reprimand Feria.
But Feria is a consort candidate, someone who can be the Queen of their country, if she were to apologize to the foreign prince despite having been wronged first is the same as lowering their country's standing, so she ignores him and keeps the conversation going with the prince.
As stated earlier the prince didn't drop wine on her on bad faith but as a test of sorts which she passed when she didn't follow him so he supported Feria's take on keeping the conversation going while praising her dress even after he dirtied it because the princess of the other country gave it to her thus using this chance to connect with both the strongest queen candidates and both countries since he is likely confident Feria is set to be the winner.
In a previous chapter the Duke had said that he wouldn't apologize to the likes of Feria because he was of higher status, that's what Feria meant, because their country is of higher status she also shouldn't apologize to the other country (they are allies but is likely the prince's country is lower in status to their own so as possible future queen she can't show any weakness to them) thus showing the Duke that she is pretty fast on her feet and different quality than them since she can play evenly in their play field despite not having any of the equipment they have, so he retired.
He is a doting parent so he is also stupid enough to not force his daughter to do the same because his little princess wants come first but it's going to bite her later for sure.