I remember seeing somewhere Martin mentions to add acid before heating as you can remove more alkalinity than intended. So I was curious if it was more so this or the boiling which can also lower alkalinity or bicarbonate (not sure exactly but with the same effect). I'll note I'm not worried about the actual mash ph as it wasn't too far out of the relm of acceptable and everything else went just fine but more so wanting to understand what lead to it. Maybe the combo and not so much one or the other alone?
The effect of boiling on alkalinity reduction depends on the amount of Temporary Hardness in the tap water. If its typical Indiana groundwater, it could have huge Temp Hardness and the boiling could have caused a substantial reduction in alkalinity. That would through off the amount of acid actually needed for that water. A lower than anticipated pH would be a result.
I wouldn't worry too much about it. It will still be beer.