Lith was surprised when Emilia kissed him so suddenly. He couldn't understand how she got herself to do this.
Emilia on the other hand wasn't feeling anything weird or off about her actions.
In the Angel Continent, elders kissed the young ones on their cheeks or forehead and it was completely normal. They did it to show their affection, love, and care that they had towards the young ones.
Emilia and Lith were close and she thought of herself as his caretaker and also his elder. She felt it was fine to kiss him as he wasn't any stranger and rather, someone close to her.
But yes, there was no need to do such a thing since even if they didn't get the discount, it wasn't like they were losing too much money. They both were extremely wealthy and they surely could afford things even without the discount.