Sentence:  Its just <WSD>fanwank</WSD> with no support in the lore - and not even good <WSD>fanwank</WSD>. As you said yourself, Malal does not exist in 40k - and he's never existed. And no, that's not a joke in the vein of 'I've never seen a stealth aircraft' either. 
Meaning of the word marked with <WSD> tags:  Explanations invented by fans (of a film series, television series, etc.) to gloss over mistakes in continuity.