Nice attempt but it looks like a joke to me .. Most of West EU zone 8 ?? Including the center of Spain ? Maybe they had that low temp once in the last 50 ? 100? years ?
Besides, to me that USDA zone system is just worthless in growing cacti .. zone 6 at 10% relative humidity may be just harmless while zone 9 and up at 100% relative humidity will kill your plants as simple as that