I mean maybe, but 401ks almost always require you to set a target fund or indicate a preferred risk level just to set an account up. So unless the commenter went out of their way to not allow their 401k to be invested, it would almost certainly be invested in, at least/lowest risk, an interest bearing cash equivalent, like a MMF as you mentioned. And MMFs were crazy last year, some earning like 7% with essentially no risk and great liquidity.