In general the concept is {INPUT_A, INPUT_B} ...> coinjoin ...> {OUTPUT_C, OUTPUT_D}

• you have input A, your friend has input B *
• you run coinjoin together *
• you get output C, your friend gets output D, but from just reading transactions in the blockchain it's not clear who got which one.

*) for some definition of friend and for some definition of together...

So yes, one could guess that you have bitcoins that were run through a coinjoin, but it's not always clear.