OK. Just a theory.
If you were low before the meal then as you are on the max doses of both Met and Glic it is possible that they combined to drop your levels way down, so even though you had the Potato etc which should have pushed your levels upwards the Meds overcame the carbs and kept you low.
I have had a very similar thing happen recently and I found it was due to being over medicated. The Glic in particular can drop you quite a lot, especially in combo with the Met.
Might be worth discussing your medication with your GP if this sort of thing happens often.
Ken