In my experience, yes. But you can't really expect a syntax highlighter to support every combination of template language and file language, so this seems reasonable enough.
I understand the limitation. Especially in the context of having the entire syntax tree parsed and stored like Zed.
I didn’t expect it to highlight 2 languages. I just wanted the Dockefile parts to be highlighted. But Zed stopped any highlighting after the first curly brace, which produces inferior results compared to the regex (assuming) based highlighters out there.