Why would we trust that source over the exchange themselves?

My other comment here was useful with other sources showing that exchanges do fake data.

https://medium.com/@nic__carter/assessing-bitcoins-liquidity...

https://www.sec.gov/comments/sr-nysearca-2019-01/srnysearca2...

The second source uses Coinbase as the standard for accuracy and compares another exchange to it...

Yes because Coinbase is a legit exchange. It also doesnt use Tether. That doesnt mean that their data on Tether volumes is correct.