He means to rebalance your 401(k) account to invest primarily in money market funds. Per the Labor Dept's guidelines for investment choices, you should have at least one.
There's another article that was posted earlier, in which a guy who claims to have predicted the dot.com collapse is getting nervous. He doesn't have much faith in money market funds, and his financial advisor has convinced him that the inflation-protected treasury bonds (also known as TIPS) are the answer.
There are bond funds that specialize in these, and you might have one in your 401(k). I have half my 401(k) assets in one, and the other half in a corporate bond fund. You may think that's too conservative, but I have long-term equity investments in other accounts (i.e. Roth IRA) to balance it out.
bingo
I like TIP's also, but a word of caution: many TIP funds have relatively long maturities. So if interest rates rise, those funds will take a price hit (bond prices tend to move in the opposite direct of interest rates).
The perfect storm for these TIP's would be if the Fed raised interest rates, but still claimed that inflation is low. Your TIP's price per share would go down, and you wouldn't get a decent inflation adjustment.
So if you think that perfect storm is possible, look at some short-term TIP funds. Some funds like that are being rolled out now.
So this doesn't really mean "cash" as in wads of dollar bills in my hands.