The author is suggesting using money market accounts as a substitute for savings accounts, and treasuries a substitute for CDs.

It is true that money market accounts have liquidity crunches (i.e. "break the buck"): https://www.investopedia.com/terms/b/breaking-the-buck.asp

Governments have a lot of vested interest in preventing that from happening, but it's not a guarantee on the level of FDIC.

EDIT: Just realized I misread the article, and they are talking about money market funds, not money market accounts, which are different things. I did not realize brokerages allow money market fund assets to be treated essentially as cash balances, which is basically what a money market account does.