I have done "some" research, much of it through this forum and honestly I haven't seen that legislation mentioned.
Don't rely too much on this forum, yes it can be useful for getting people's subjective views and it's fun etc, the personal touch is nice, but it's not the best place to be looking for the answers to legal questions. Some people can give misleading answers or out of date information.
I would suggest that you start using Google Translate and google your queries in Polish, then copy and paste the answers to get the translation. You'll find all the up to date information you need. There are even 'ask a lawyer' a question sites.
With regard to the ROD plots in particular, there are two ways to acquire one. Either directly, from the Association that manages the land, or from an individual who leases a plot. If you approach an ROD management board, it's unlikely that they will sell one to a non-Polish person, especially if they suspect you want to live there. The ROD plots were particularly designed to give urban dwellers access to healthy, outdoor activity, the ability to grow their own fruit, flowers and veg. They are basically recreational plots and not intended as dwelling places. Legally, you can only have a building of up to 35 square metres on them. I have seen some up to 60 square metres, but you could be asked to take it down, so I wouldn't buy a plot with such a building on it.
he fact that it is above a certain size/area?
Yes, even an EU citizen can't buy land above 0.5 hectares for his permanent place of residence in Poland.