Eastern food or Western food can be a big decision in Japan with multiple people involved. For breakfast you've got fish and rice and miso soup vs bacon eggs and toast. For dinner it's, say, Japanese pub with stuff like yakitori, or French or Italian or just a place like Denny's or Sazeria that's basically tons of Western food (with a little Eastern). In North America it's like 'Hey guys, we getting pizza or sushi?'
It's such a big deal that there are several shows about it, like the one you mentioned. But really, the tl;Dr is that Subaru is Eastern food and Bellanoa is 'Western' food since she's not East Asian.