You're misreading. This wouldn't get the $1 fee. "We're giving you 20 TB (TWENTY) but don't you dare use more than 2 TB (TWO)"
It's a classic web host reseller technique of overselling and having it backfire.
That's only a problem if they cut you off. If there's a defined (low) fee for overages then I don't understand what the problem is. $1tb is very well priced. AWS/GCP charges from the first byte after the miniscule free tier.