That's a scam. There is a trend that I have seen going around online called coinbase wallet loading and coin flashing. That is obviously what the person did to you.
Let me ask you: how did they do that? Did the person give you a smart contract address to add to your Coinbase wallet and import it? Because they have a specific smart contract for such a scam coin, you will need to manually enable it before it will show up on your Coinbase wallet, and once you have enabled it and they send the fund to you, it will be visible on the wallet only, but you can't swap or even send it out to another wallet, but still there will be value attached to it.
Well if you can simplify to beginner terms for me what your question is that would help me answer. The person said they needed me to download coinbase app onto my pc or phone. When I did that he asked for my new wallet address I think, and then he sent me some funds into it.
I saw there was a transaction that was successful and then he told me to transfer the funds into my ethereum account. Then I had an error on the app that said I don't have an ETH account. So he was trying to explain to me I needed to create one, and then add additional funds into it to "enable" it or some jabber. It was happening so fast I didn't understand what was going on. He tried to tell me I had the money but its locked into the Tether USDT Ethereum network and to transfer to CAD I had to deposit some 3,000 dollars into another ethereum account to move it, the address he gave me from his end.....I dunno I said that makes no sense and sounds backwards to me. Add money so you can access it sounded like a scam to me.
And yes I can only see the USDT tether amount on the wallet only, not my assets page. I found a tab somewhere looking up on my profile and showed up a list of assets. The section was "Hide Assets" and said my 10 dollars or so of ETH in bright, then below had a line that said SPAM and a bunch of transactions apparently, and the bottom of the list was Tether for XX,XXX dollars.
I just later gave up to talking to the guy, and been ignoring him for a few days researching what was going on, and here I am.
Hope that makes some more sense.