What does blocking players actually do?

I played against someone who was an absolute toxic, sweat. The type of player that back passes and does skill moves while leading 4-0 in a Live Event.

I blocked him afterwards.

A few games later and we're back in the same lobby. This time I got the upper hand and gave him a taste of his own medicine. He proceeded to quit. 😂 I guess the lesson here is "he who laughs last, laughs best."

But I still don't know why we were matched together after I had blocked him.