I think your sentence sounds VERY natural in informal, spoken English (I am British). The grammar might not be perfect, but this is still how people speak!
You just need to add "don't" (because it's a negative statement: "...can't be..."). The last bit ("I don't think"/"I think") would usually be said as a rhetorical question.
A What kind of food is this?
B I'm not sure. It can't be Thai or Indonesian, I don't think?!