In almost all mammals the red blood cell is a round biconcave disc. Camelid erythrocytes are elliptical and flatter, and they lack the central pallor typical of other species. Under dehydration, when plasma volume falls and blood becomes more viscous, the oval shape and small size help the cells continue to traverse capillary beds.
The more unusual property is osmotic resilience. Camel red cells can take up water to well beyond their normal volume without haemolysing, which matters because a rehydrating camel may drink a very large quantity in a short time, briefly diluting the plasma. A cell with an ordinary membrane would rupture under that osmotic load.
The hump is not part of this system. It stores fat, not water, and while metabolising fat does release metabolic water, the oxygen required to do so costs more respiratory water loss than the reaction yields. The camel's real water economy comes from concentrated urine, dry faeces, a body temperature allowed to swing several degrees across the day, and nasal passages that recapture moisture from exhaled air.