Most 1970 model 340 4bbls were painted Street Hemi Orange. I say most because you can never say "all" or "never" with Chrysler.
All the other LA engines that year were Blue. So you can see how the odd mistake could be made.
340 4bbls continued to be painted Street Hemi Orange until April 1971 when they started painting those blue as well.
Of course someone could have swapped your 340 for a 318....