Type 1 Low blood sugar after huge meal

I just had a massive bowl of clam linguine followed by tiramisu and a coffee. Before the meal I had a reading of 6.4 an hour and a half after my reader says 3.4 and the arrow pointing down. Pricked my finger and it reads 5.5. same amount of insulin as normal. Any clues ? I know there is a delay with libre but the prick test was low after all that food.

It did about 5 hours after. I no I'm not meant to eat big bowls of pasta and a desert but had a meal out on holiday and thought I would have some freshly made pasta. Which I must say was worth the panic delicious

Thanks for a reply curlyJ