להודיע כמה ארך אפים לפניו (פרק ה:כ)

The Mishna already says how much “ארך אפים”- ‘controlled anger’ Hashem has when listing the ten generations from Adam till Noach.  Why does it need to repeat by mentioning the ten generations from Noach to Avraham?

Since the first ten generations were before the Mabul (great flood), no wonder Hashem was an ארך אפים since that generation couldn’t learn from Hashem’s punishment. However, the ten generations from Noach to Avraham witnessed the sentence from the Mabul’s generation, and they didn’t learn from Hashem’s wrath. Thus, Hashem contained his ‘ארך אפים’ on these generations too!