No, this is wrong. Withholding information is definitely a lie by omission and comes in many flavors.

Failure to report - Knowingly withholding information about a severe crime.

Obstruction of justice - Intentionally hiding or omitting details to mislead authority.

Accessory after the fact - Omitting or lying about information to avoid becoming an accessory to a crime

Material omission - Omitting crucial information in relation to a financial crime AKA fraud.

Your silence in these situations is most definitely a lie. I think you are stuck on only action being considered a lie, but inaction is considered a lie by omission in these situations. This is a legal definition, so please keep that in mind.