I can not think of any especially convincing reason, but I'll try. I'll just copy Malack's Death-is-Neutral speech:
:You know, neither gods of Death nor their clerics are necessarily Evil. That's a common misconception. || If anything, Neutrality suits them better || If the power of Death were truly Evil, it would take only the pure and heroic, wouldn't it?
Now, the crux here seems to be why he didn't use "us" instead of "them". The only suitable reason I see is that he was too polite to put himself on the same level as his God by his speech. He wanted to avoid sounding like this bodyguard: "Our mighty king Roy doesn't wear golden armor, neither do his bodyguards. We like to look modest."
Or much more simple: the Giant wanted to put some ambiguity about Malack, and made him phrase it so that it could go either way. And did not bother about in-character motives. I think it happened before; that he made something to happen without thinking about the exact in-universe process. (Like, Xykon getting out of Lirian's cave)
Now, I only thought about this because I consider the alternative, that Malack is LE and this is a deliberate and cunning ploy on his part, less likely since it contradicts Malack's ordinary behaviour.