WWII bombers were largely ineffective against rail lines.

There are a number of reasons for this. The first is that WWII bombers were not accurate enough to reliably hit a rail line. Keep in mind the very nature of a set of rails--they are a ribbon of infrastructure mere feet wide that snakes through the country. Now we add the difficulties of WWII bombing that resulted in most bombs ending up nowhere near their intended target. Specific factories were often missed by the bombers tasked to destroy them, and there were many times in which entire cities were missed by the bombers. The 'solution' to this difficulty was to send more bombers (again, at great expense) so that you could drop more bombs in the hope that one of those bombs would hit its target. This was somewhat effective.

There were indeed operations undertaken against German rail lines. Most prominently, they were targeted as part of the 'Transportation Plan' prior to D-Day. As reconnaissance during the war indicated and surveys after the war confirmed, there was some success for a time. Rail lines, if targeted with large numbers of bombers, could be disrupted--but only for a short time. But unless a bridge or viaduct was somehow heavily damaged or destroyed (something only 'tallboy' and 'grand slam' bombs very late in the war had any real chance of accomplishing), the railroad would be repaired in short order. Basically, most of the time the trains were able to roll through the targeted area in 24 hours. (This is covered in a good bit of detail by Christian Wolmar in Engines of War) This is partly due to the aforementioned difficulties in targeting rail lines, but the Germans also had dedicated forces to repairing railroad damage. In addition, these units would compel local people to assist in the reconstruction of the rail line. Further, outside of bridges and viaducts railroads are basically piles of rocks and gravel with a little wood and steel beams on top. This means that low-tech solutions were perfectly suitable to fixing the damage caused by relatively high-tech instruments such as heavy four engine bombers equipped with every modern piece of equipment. German railways only collapsed extremely late in the war, basically when every other service had also shut down and the government had effectively collapsed.

So the practical impact of Allied bombing on the death count in concentration camps was negligible. Damaging railroads was difficult, rarely had the capacity to stop rail traffic for a matter of hours, and German railways proved to be very resilient despite a lack of triangle junctions.

I believe you are. Their comment also relies heavily on the idea the Nazi's gave a damn. I'm not an expert but I think if the railways were heavily damaged the Nazi's would have been concerned about using them for things like transporting war materials, human beings, and belongings FROM the camps long before they would worry about feeding their prisoners. Besides the guards didn't seem to have any problems getting food or drinks for themselves into the camps.