That was my first encounter with the difference between how "impact" is used by impact evaluators, and how the term is used in the traditional monitoring and evaluation (M&E) field.
To get a sense of how traditional M&E folk view impact, here is the definition used by my talented colleague Dominique, who oversees monitoring and evaluation for the Ministry of Finance:
"The long-term, cumulative effect of programs/interventions over time on what they ultimately aim to change, such as a change in HIV infection, AIDS-related morbidity and mortality. Note: Impacts at a population-level are rarely attributable to a single program/intervention, but a specific program/intervention may, together with other programs/interventions, contribute to impacts on a population."
Notice that Dominique's definition specifically points out the difficulty in attributing impact to specific interventions. This is pretty much in direct