If you don´t believe it, than go buy it and test it for yourself. As far as I know, if the datsheet says it can work up to 70°C ambient when mounted in horizontal position (on a wall, air free flowing by convection from bottom to top through the mesh) then it will, and probably a bit more. Our customers would tear us to shreds if such specs were not true. But also note the derating on page 2, it is a convoltued way of saying it drops from 40A at 60°C to 25A at 70°C ambient.
(I design I/O modules in similar form factor, and know how the typetest goes and that the datasheet always has derating if the product cannot provide full performance over the full temperature range)