That is literally what that means. Market caps are what they are because everyone who thinks it is worth less has sold and everyone who thinks it’s worth that or more will buy. There’s some outliers but in general these coins are trading their entire market cap over the course of maybe a month or less. Liquid generally means short term, if you can sell it for cash in under a year then it is liquid. Sure if you tried to sell all coin today in the same minute you won’t find a buyer but over a month this happens all the time.