ermm ! hello ! what did that mean

sooooooo this was a few days ago i think but i was sitting with my friends and umm. one of them just randomly put her hand on my shoulder for like no reason for a whole second and i was so confused and didnt know what to say so i just went "what !!!" and started laughing and then she started laughing too. nobody else acknowledged this. WHY DID SHE DO THAT !!!! WHY DID SHE RANDOMLY DO THAT WHERE DID THAT COME FROM!!! WHAT COMPELLED HER TO JUST DO THAT IT WAS SO WEIRD AND OUT OF NOWHERE..................................  like do you have something to tell me.......... (joke) (she was probably just trying to be funny and im looking too deep into it) 

anyyyywayy im honestly glad im friends with her + the whole group they are all so nice to me compared to my ex friends from last year

and omg people also need to stop randomly touching me its scaring me a little. cuz first it was her and then a diff day another friend of mine started aggressively patting me on the back for no reason either. WHAT DID I DO !!! unhand me!!!!