Isn't this terrible advice?
I'm suspect What 3 Words works on a vocabulary of about 40k words, which probably matches an English speaker's passive vocabulary. (The earth has an area of about 5.1e14 square metres; 4e4^3 is 6.4e13, meaning that a W3W square is just under 8 square metres, which seems about right.)
Let's be really generous and assume someone asked to come up with three random words is able to pick each word from a 50k word vocabulary (I suspect, in practice, an awful lot of people would be picking, from an immediately accessible vocabulary of 5k words or less). So, like W3W, you now have 6.4e13 combinations.
On my keyboard I can comfortably type 88 different symbols (26 letters + 10 shift-digit symbols + 8 punctuation = 44, all of which can be shifted to give another 44).
Now my maths might be wrong (l seem to have some kind of long Covid neurological issue going on, so please be gentle!) but as 88^7 = 4.1e13 and 88^8 = 3.6e15 that means even a good three word passphrase would have about 50% more entropy than a 7 character password whilst an 8 character password would have 50x more entropy.