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Why did Mitsuha's face go red when Taki told her that he drank her kuchikamizake in Kimi No Na Wa?

This question has been nagging at me all night. So, can anyone explain what "kuchikamizake" is and why it pertains to this particular scene?

Kuchikamizake ("mouth chewed sake") is the sake produced by using saliva for fermentation. We see Mitsuha making it as part of her duties as the Shrine Maiden, during the festival.

Her face went red because Taki drank the sake that had her saliva in it. In addition, her own classmates considered it gross when she was making it during the festival, so the contrast to Taki might have made the feelings stronger.

As TheGamer007 mentioned, Kuchikamizake 'is a kind of rice-based alcohol produced by a process involving human saliva as a fermentation starter.'

Here, however, is where my answer differs.

Why did Mitsuha's face go red when Taki told her that he drank her kuchikamizake in Kimi No Na Wa? This was explained by Makoto Shinkai himself here. To quote from the article:

'The film’s oddest moment comes early on, when Mitsuha, as part of her Shinto ritual, chews and spits rice into a jar to make a primitive form of sake, fermented using human saliva. Later, Taki drinks the sake. Shinkai has said that he intended the scene to represent an idea common in teen anime, the “indirect kiss,” in which one drinks from the same container as one’s crush. But the image of a teen-age girl dribbling milky liquid from her lips has raised eyebrows. Pressed during a December TV appearance, he admitted that “saliva is a fetish element for a lot of teen-age boys.'

If you have seen other anime or read other manga with romance involved, it's a common occurrence for girls to get flustered or make a big deal out of boys drinking from the cups or glass they just used with their saliva in it, for example, as they see it as an indirect kiss. This question was also asked in another forum site, that's why I found out about that news article.