Are there any other meanings for "belie??" [closed]

Belie has two meanings. The first is to betray or contradict, in the English idiom, to give the lie to:

Court transcripts showed that his sworn testimony belied his later claims.

The second meaning is to give a false impression:

His youthful appearance belied his age.

The second meaning is applicable to the translation. The sense of the original is that holding the weapon straight and without twitching is an indication of concentration. The meaning of the translation is that such a stance is an indication of a casual manner, which is not Dyne's mental state: he's actually concentrating hard, indeed at an "impressive level", and thus the casual manner gives a false impression.

A straight arm and a steady aim doesn't strike me as casual, so perhaps the translator misunderstood the passage. Or misunderstood what belie means, thinking that he was expressing something like

He held the SG 550 straight, without a single twitch, and was thus beheld to have an impressive level of concentration...

That's impossible to tell without consulting the translator.