In that particular court case, yes. But the key point is Congress may regulate intrastate rates if they affect the interstate rates that Congress is regulating.
You would agree, however, that the objects of commerce are affected by the rates?
The objects themselves are not. The buyers and sellers are.
Congress did not regulate the intrastate rates. They regulated the interstate rates. The corresponding affect on intrastate rates was do to the way the rate schedule was contrived by the railroad. The could have kept the intrastate rates the same in spite of the regulations being imposed on the interstate rates. They simply chose not to.