Dave is right I'm afraid on all points mentioned. 6v6gt...also good points. This traffic light system doesn't represent the same ones we encounter but is a good exercise in making truth tables etc. We know that actual systems have more features like left turns... right turns.. timers.... underground car detectors etc.
If a student realises there are other things that could be added in future.... then that's fantastic progress. The teacher did a good thing by making the exercise linkable to something practical .... ie. traffic lights. We all got to where we are by.. as dave mentioned.. crawl before walking.