I think you're overthinking the question. My interpretation is that Peters & Peters want you to tell them about any achievement (personal or professional) that added value.
You could structure your answer using the STAR/CAR technique and maybe have a sentence of the overall impact.
For the "working environment" you could give a directly related example i.e. you may have devised a new system at your workplace that allowed them to track something better which resulted in your promotion/bonus, etc.
Or, for the "working environment", it could be that you give the example of an extra-curricular that helped strengthen a skill that you now use in your work/academic life.
Hope that helps!