Is this an ego?

Your senior is supposed to fill in a document. He's busy, so he can't do it. He asked you to help fill it and send it to his work partner—a stranger to you—in a Telegram group where there are only your senior, the stranger, and you.

You wrote a nice message addressing that stranger and sent the document file along with it.

The stranger saw it. He didn't say a thing about it, but went on to talk about something else with your senior. Even your senior kept referring to you to handle it, the stranger still insisted to talk to your senior, but not you. You were just there in the background.

In your mind, you questioned yourself, "Is this person ignoring me? Who does he think he is?" You were kind of pissed. You probably felt like you were offended, and your self-importance was decreased. You hated that stranger and swore you would never talk to him/her.