It implies they think he either lied or omitted crucial information.

Lying by omission is still lying, and is especially a concern when you have a duty to the people who are deceiving, such as an executive has to their board.

Isn't that considered deceit rather than lying?[1]

[1] ChatGPT "lying is defined as intentionally making a false statement. If you are omitting details but not actually stating anything false, this may not strictly meet the definition of a lie."

That's corporate for "he's big ol' lying ass liar who lies."

Correction, its: "he's big ol' lying ass liar who lied to us."

Point taken.