Flexbox - Review: Flexbox

Hello arrayjumpers,

I have just completed the the last exercise of Flex box - Flexbox review.

I notice on Step 4 of the instruction that we set DISPLAY: INLINE-FLEX to the .col class.
But I tried also with FLEX and there is no difference. Why is that?
I expected that if the .col class is FLEX (that is block), other columns would not be allowed next to it.

Why are the columns aligned next to each other even though I changed the display to flex?

https://www.codecademy.com/paths/web-development/tracks/getting-more-advanced-with-design/modules/layout-with-flexbox/lessons/learn-flexbox-l/exercises/review

Thanks!