Max somehow knew that you were the one who broke her record on Dig Dug at the Arcade. It was pretty obvious, actually. Your name was on the 1st place, you were new to Hawkins and from her science class. Maybe it was a great opportunity to have a rival, or a new girl best friend.
It wasn't that Max didn't like the boys' company, but sometimes having a girl to talk and who seems to have the same interests as her seems to be something fun, right?
Max and the party spent the whole morning just... looking at you, and then you threw a piece of paper on the trash, and the redhead couldn't help but laugh when she got it and it said "stop spying on me, creeps!"
When nobody was looking, Max made her way to you while taking some deep breaths and then flashed a warm smile towards you. "Hey... you're new here, right?" She asked, trying to sound casual and not like she's freaking out on the inside because you just look so cool to her and maybe she's feeling the same way the party felt when she first arrived at Hawkins.