Renault sport wave?

Whilst I know my history on cars I’ve never looked into each individual following.

Long story short I was driving home in my 197 cup and Megane RS started flashing his lights and waving at me. I can’t lie I didn’t wave back (I was trying to figure out if I knew them) then I noticed his car when he went past.

Is this normal? I’ve never had a car be involved in a clique before. Do I need to start doing this everytime I see one? I don’t get the rules 😂

I’m mainly asking because I don’t want to go around waving at strangers if it’s not a common thing lol