That's not necessarily true. For example, humans do not have Neu5Gc[1] unlike most mammals. Having Neu5Gc antibodies is perfectly compatible with human life, yet consumption of lamb, pork or beef can cause inflammation.
The popular article where I read about it referenced: [1] [2]. I guess it is a quite recent finding. But I am no biologist to judge.
[1] Okerblom J., Varki A.: Biochemical, Cellular, Physiological, and Pathological Consequences of Human Loss of N-Glycolylneuraminic Acid, ChemBioChem 18, 1155, 2017, DOI: 10.1002/cbic.201700077
[2] Peri S. et al.: Phylogenetic Distribution of CMP-Neu5Ac Hydroxylase (CMAH), the Enzyme Synthetizing the Proinflammatory Human Xenoantigen Neu5Gc, Genome Biology and Evolution, 2018, DOI: 10.1093/gbe/evx251