why I can open a contact from imessage?

Are you using the same AppleID? If yes, are you syncing contacts via iCloud?

You're post is a bit confusing. Did your friend share a someone's contact information with you so that you could add it to your contacts? If so, what is the problem you're having? What are you trying to do? What happens when you try?

i sorry hear this, iPhone very smart and u can open contact friend send iMessage it normal