In my humble opinion your response was 100% correct.
A WBO2 can be a helpful tool, and it can help in situations where we aren['t sure, or happen too quickly for us to know the effect of a change. For example if you had the engine on a 1/4 mile run or a dyno, a logger could show us whether the AFR was staying flat in top gear or trending lean or rich with increasing rpm and wind resistance.