Depends who put the engine in there. If the car is a 1999 it may not of actually had the engine switched, they cam with both phase 1 and 2 that year. If you KNOW that it was swithched, was it switched at a dealership, or in someones garage? Ask some questions and see if they give you a straight answer.
Most likely replaced due to piston slap if it was done under warrenty at a dealership. If it was don in someones garage, you open all sorts of new possibilities like hydrolock bending a rod, a bad tuning job on a turbo kit damaging the shortblock ect ect ect. Otherwise maybe they just wanted to eventually turbo the car and wanted the more stable crank for the car and just never got around to turboing the car.
Ask for reciepts, or proof that the job was professionally done, unless you are a mechanic yourself, or plan to take the engine apart soon anyway.