Although Glasp can probably elaborate on this, as it was his baby.
Consider them somewhat like appraisals. In your pasted message, you 'believe' does not mean that you 'know'. For example, 'guessing wildly' if someone sees you or not would tell you that you're probably not completely accurate with your estimation.
Also, there are occasions when you might see someone sneaking, but you don't see them hiding, etc.