Romanians also say ”Cartofii sunt de la frigider”
It suprised me, I never saw that translation...
It is used to suggest "cold", mostly with beverages, somehow equivalent to "chilled"
So is the deifinite article dropped from the noun when preceded by a preposition? why frigederul not used in this sentence?
Yes, with some exceptions such as preposition "cu" (with)
why not dinspre in place of din?
Technically "from" can also be translated by "dinspre" as in "vântul bate dinspre nord" (the wind blows from the north) but it does not make any sense in the present case.