I met a buddy in the gym today, and his muscles are great. I wanted to add him to WeChat, but he refused. I didn't mean anything. Did he think of anything else?

If you add him, of course he will receive the application, so he knows you want to add him. If the other party sets "No authentication is required to be added as a friend", the default is to reply to you, or if you apply, you will appear in the friend list, and maybe he won't know that you added him.

Now that everyone rejects you, it means that he knows you want to join.

If you mean that he knows you are applying (because you don't use an avatar on WeChat or the application doesn't indicate who you are), you may not know who is applying, but you will definitely see your nickname.