Free store item that is paid in minecraft for windows 10

i was searching for free items in the store like 10 years,etc but i saw the deep sea mashup
and i downloaded it (it was for free) 2 days after that i was going to play it with my brother
and he could not join it, i thinked maybe if he download the item it will work
then i saw it was paid and not free
and i got it for free
what happened?