Compliment comparison

I have examined the same compliment from Satoshi to Serena. She has torn her dress during her preparations for a perfomance, and the compliment from him was a good way to comfort her after her struggle with it. I think this could be its reason. It was care.

But the question is: what was his reason behind giving this compliment to Hikari? She wasn't struggling. On the contrary, she was like in the heaven in it. She didn't need the compliment but she got it. And Satoshi isn't a guy who often compliments girls' dresses.

A few more details about compliment episodes:
- Satoshi complimented Serena with his eyes closed, but he complimented Hikari looking straight at her.
- Satoshi didn't look stunned after he saw Serena in the dress, while he was visibly stunned after he saw Hikari in the princess dress.
- Eureka reminded Satoshi about Serena during Millefeui's perfomance, while Hikari popped up on his mind without Takeshi naming her - while being away from Hikari, Satoshi was worried 'if she was doing well'.