

This is how bilinguals of any languages speak so it’s not surprising. I read some study a while ago that said that if you have more than one native language it kind of works in your brain as if you have just one language, but it has all the stuff in it from both languages, which is why it’s so easy to switch. I’m sure you know that some things are easier to express nicely in some languages, or don’t translate easily, so it’s quite useful to do this.
I think bilingual in the linguistic sense is more if you grow up using both languages a lot in early childhood, and especially if you use both in the home, and not so much about the final fluency. I do this kind of rapid switching between Dutch and English because I grew up speaking Dutch at home in an English speaking country. But I wouldn’t say my Dutch is really perfect, I am missing quite a lot of vocabulary after decades in an English country and I don’t know a lot of formal/polite speech. But I can easily relate to how they are mixing the languages, it is quite natural. I also find it disorienting to switch to languages I learnt later in life, even one I learnt to a very high level, and I don’t often mix at all with that one.