He that would live in peace and at ease must not speak all he knows or all he sees.

Not everything true needs saying, and the urge to say it is often about relieving yourself rather than informing anybody. Holding something back is not dishonesty; it is recognising that most observations cost more to deliver than they return, and that you will be the one living with the consequences. There is a limit to this, since staying silent about things that harm people is a different matter entirely.

Before passing on what you noticed, ask what it will change. If the honest answer is nothing except how you feel for a minute, that is a good candidate for keeping to yourself.