"Through" or "return" catering is common practice throughout the industry and is nothing new. But, it takes more QC by the catering contractor. UA's simply doesn't do that and the concept routinely fails.
Ice is always available and it is more than likely that if ice ran out, that the forward FA who should have grabbed it off the jet bridge, failed to do so. Again, sloppiness.
But, conceptually, this is fine. It is rarely a direct cost savings.