The phrases مَا زَالَ الشَّيْطَانُ يَأْكُلُ مَعَهُ and اسْتَقَاءَ مَا فِي بَطْنِهِ are part of the narration. Their meanings can be explained without inventing a scientific or physical account of unseen matters.
This account reinforces the earlier command سَمِّ اللَّهَ. The first meal-related report teaches remembering Allah at the beginning; the second explains what to say upon remembering after an omission.
When another person forgets, a gentle reminder is more appropriate than ridicule.