To be 'free floating', the barrel would need to have no points connecting it to the the gun anywhere forward of the point that it mates with the receiver. Because of the FS2K gas-piston assembly, I would consider it to not be a floating barrel.
The gas piston provides a link back to the reciever foward of the chamber, but other than that it is free floated, the collar that fits loosly around it has clearance so technicly it is as "free floated" as a gas piston is going to get.
Regardless of the gas piston assembly, a free-floating barrel would not be affected by any forces exerted from holding the weapon while shooting. While the PS90's barrel sits "loosely" in the receiver, I would not consider it to be a pure free-floating design due to the fact SOMETHING is touching the barrel and would affect the barrel harmonics. The good news is that I don't really see much of an affect on precision with light-profile non-free floated barrels (such as 16" M4 barrels). FNH USA has even said that the FS2000 and PS90 were never intended to be target rifles.