I don't understand. What were they buying and selling? FOMO or FUD?

For the average person, you wouldn't notice a huge difference. Especially now, where online banking has progressed and is the norm. Credit unions tend to have lower interest rate loans and lower fees, which is better for the account holders/members. The members are considered "owners" and the aim is to provide as much benefit to the account holders as possible, vs your BoA/Chase mega banks where profit above all else is the goal. Credit Unions have fewer physical branches and branded ATMs, but instead use a network approach to ATMs, even waiving/reimbursing ATM fees most of the time. For example, I typically use ATMs at any target or CVS location, so no less convenient. If you need in person services, then you likely have less options if you bank with a CU. Moving past the "Fiat bad" stigma, Credit Unions off the same deposit insurance guarantee up to $250k USD, only thought the Nation Credit Union Administration (NCUA) instead of the Federal Deposit Insurance Corporation (FDIC).

In short, for the typical user these days accustomed to online banking and not in need of physical branches/in person services will have just as much safety holding Fiat at a Credit Union and receive better savings rates/APY, and lower interest rates on loans. Plus the added benefit of avoiding our defacto nationalized mega banks.

Edit: I should note that not all CUs are equal, so if it's a small community chartered CU, then you may have less financial products available. But most typical/reasonable sized CUs will fell just the same as banking with Chase or Wells Fargo, etc.

Source: been at a CU for a long time and also know people who work for a decent sized/top 5 CU in my state of residence.