There's nothing inherently wrong with the title Android Engineer. An Engineer is:
- a person who designs, builds, or maintains engines, machines, or public works.
A person who designs, builds, or maintains Android hardware or software would be an engineer, one who specialises in Android systems, so they could certainly be called an Android Engineer. A Google search for the exact title "Android Engineer" returns 396,000 results, which is a pretty solid amount.
If you're not certain that the actual person in question has that skillset, that's a different matter; but there's certainly nothing wrong with the title itself.