It is my understanding that Stack Exchange determines what syntax to highlight in code blocks based on the question's tags. If no language tags are specified, the behavior is to skip the highlighting entirely. (For more details, see this answer and this help section)
An example of a question with code blocks but no language tags is The moderators have decided to have a little yuletide fun, join us will you?. All the code blocks have no highlighting, as is expected. But not so in the Android app:
Not particularly concerned, just pointing it out for behavior parity purposes.