I very much doubt it. There was probably changeover period when the guy who orders the card for the boxes ran down his stocks of 350W boxes so they only had the 450W boxes but they were still building with the 350W PSU. They probably had a meeting about it where the Technical/Compliance Manager said "That's dodgy, we'll only get complaints - and possibly prosecuted" and the Production Manager said - "Nah - the customers are all stupid, they'll never spot the difference, it's a commercial decision and we're shipping them". Not that that's ever happened in any factory I've ever worked in, you understand
OR
You bought a return where some smarty-pants had a 350W, then bought a 450W, swapped them over and then returned the new one with the 350W PSU in it. That happens far more often than you would like to think about. Was it a B-Grade or Clearance item if you don't mind me asking?