The information in the rules represents things the characters would or could know.
No it doesnt. Any more than it tells them when they meet a Human Farmer (a Commoner NPC) that he's Neutral 'because that's what the Monster Manual says he defaults to'.
While we (the players) might be in a (somewhat) privileged position to glance at a Characters character sheet or write up and see that creatures alignment as 'evil', the characters in the game are in no such privileged position.
In much the same way you and I, right now, are debating 'what' exactly is evil, so would the PCs in the game world!
And in much the same way, in the game world an evil creature itself might genuinely think its a good person (as would many people who know him) despite that not being the objective reality as you and I know it.
Consider a Vengeance Paladin committed to the wholesale genocide of Orcs. He's driven - he offers Orcs no mercy, pity or remorse. He engages in torture, murder and worse to bring woe to the evil scourge of Orcs. He tosses mewling Orc children on the burning pyre because 'nits make lice' and to save generations to come. He rides into villages with an army of devout followers and slaughters every Orc he can see, crucifying the leaders as an example to others. He has the survivors rounded up and sent to work camps, where they are forced to create weapons for his armies, and tend crops for them, before they are led to mass graves and executed.
In his mind he's a Good man. He genuinely believes it to be so. He works towards a 'greater good'. Many of his men think so as well, having seen the savagery of many orcs up close and personal.
Of course if you or I (in the real world) looked at his character sheet, he's Evil with a capital E,
because he is no different from the Orcs he enslaves and butchers.