How can I tell if regulation is at the transcriptional or translational level?
From the Methods section:


  Human TfR in plasmid cDNA was a gift from Tim McGraw (Weill-Cornell
  Medical College, New York, NY). Human TfR cDNA was subcloned in frame
  with EGFP in the Clontech pEGFP-N1 vector at the XhoI and BamHI
  restriction sites.


This TfR-GFP fusion protein does not have the endogenous TfR promoter. So it is not likely to be regulated by any TF that would directly regulate TfR transcription. 

So they conclude that Rabenosyn-5 does not specifically regulate TfR expression.