Remember: 40k has no canon.
This is just one of the examples in how the sources may differ -- just like how in the Horus Heresy novels, Magnus never managed to deliver his warning, in direct contradiction to GW's own Index Astartes articles as printed in White Dwarf. Not to mention the whole business with the Primarch's power levels, or the silly Perpetuals.
The only thing that irks me at this point is that these novels and the deviating information contained within are more popular and thus more widely known than the original fluff by Games Workshop themselves ...