I think the references that you are using were from back in the early 2000's when France bought up a bunch of banks.
Not only banks but also French Télécom bought the TP S.A. and other giant French
companies invested in Poland (Vivendi Universal, Carrefour, Casino, Crédit Agricole,
Saint Gobain, Auchan). The cummulated French investments in Poland in 2005 were
about 15 billion Euro (ahead of Netherlands, Germany and USA). I don't have any newer
data but I can recall that even recently, in various press articles and radio programmes,
France was referred to as the largest foreign investor in Poland.
NBP only has the 2008 report online.
It looks like they only give data about capital flow and direct investments in the single
2008 year only. I meant the overall value of all assets and investments that a country
has in Poland and apparently the leader is still France.
Anyway - it's not a big deal for me really. As far as I am concerned it can be Germany,
Russia, Japan or USA - it's all the same as long as they invest their money here.