Runeglaive cancelling blind bug/intended effect?

Long Store Short, I was playing Teemo for the first time in Ages. In 3 seperate fights against an AP Runeglaive Ekko, I blinded him and his basic attacks immediately following the blind connected with me, triggering his 2nd and 3rd stacks of his passive. I'm assuming this is because Runeglaive turns a basic attack into magic damage? And is the turning of magic damage supposed to make his basic attack bypass a blind?