In AE we would also say electronics engineer. (I have worked with many of them and hired several.) I agree with heypresto that in the phrase "electronic engineer" the word electronic is an adjective that describes the engineer. It does not say what sort of engineering he or she does. The professional field is electronics, not electronic.
If you can do this in a polite and respectful way, you might show this thread to your teacher.
I have the same question about Electronic/Electronics Engineering, but given what you said, what about a mechanical engineer? Following the same reasoning given in these replies, a mechanical engineer wouldn't be an engineer who is made of mechanical parts? Still this is what you call them. Do you think this "adjective" is right for mechanical engineers but not for electronics engineers?
Electronics engineering is a modern specialization in the older field of electrical engineering.
While we're playing with "logic": Electronics engineers make electronics. Mechanics engineers make people who fix cars.
I agree that it is normal to say electronics engineers which designates people who design and prototype chipsets and other electronic devices. However in BE one does not say mechanics engineers. Mechanical engineers would be horrified that they they are thought to either fix cars or train others to do so. Mechanical engineering is close to physics and much of it is calculating stress factors, design limits etcetera.