Translation:He did not say hello, but bowed in front of the teacher.
Actually, per my (large) dictionaries this sentence IS saying bend over in front of… while the term riverenci should be the term used here. Riverenci shouldn't even need the "in front of…" bit.
So: "Li ne diris saluton, sed riverencis la instruiston." Is the response which has cost me several points on this sentence. The bending over form sounds like some uncultured, uncouth schoolkid describing the foreign exchange student's first entry into class.
Referencing yet another dictionary, I found that klini = incline, cause to bend, slant downwards. But that kliniĝi = Bend down (forwards), bow down, crouch, lean, stoop.
Another dictionary gives us klini = tilt, incline. (no reference to -iĝ-)
This is why we should never depend upon just one dictionary, if at all possible.