Non-rotating end cap roller bearings (field lube, oil or grease) typically have thicker bearing boxes, most notably those made by Hyatt and to a lesser extent, SKF. The 'non-rotating end cap' description was/is from the BNSF Sytem Special Instructions, IIRC and not my own supposition. Further research would also indicate handling instructions for plain-bearing equipped cars, most notably they are prohibited in interchange. Let me know what happens when a plain-bearing equipped car passes over a bearing detector.

As for the signifcance of the bearings, not only is the thickness of the steel thicker because of the bearing box casting, there is also occasionally a bar between the pedestals that retains the bearing housing in the pedestal in the event of a wreck. This bar may exclude a good reading. I cannot, with great certainty, explain the physics, only that these bearings have presented problems in the past, and there are/were instructions regarding them.

If I had to guess, I would say that the IR reading is looking for a range of bearing temperature, adjusted for ambient air temp. Should the reading fall below the miminal expected reading (due to the significantly large mass of steel of a cast bearing box?), I would presume the logics would prompt an error message. This is not my field of expertise, however.

In any event, if the B/O codes mentioned on this thread are accurate, the root issue is not the bearings, and this becomes just a side thought to the main problem.