It's scale alright-- approximately Q scale, or 1:43.5. A little bigger than true O scale. Put it next to a brass Weaver A5 and you'll see the difference. In all fairness, Lionel's 0-4-0's going way back to the prewar 1662, 1656, etc. were all slightly oversize.
If you want a true scale model your only choices are Weaver and MTH. Be prepared though, because this was a small loco in real life.