Smell is one of the five senses.

We experience and understand the world through signals that are received by the senses and interpreted by the brain - and both stages are subject to distortion.

And so, knowledge from the past, mixed up with assumptions about that knowledge, which may be more or less appropriate, is used to augment information provided by the senses.

Which means that our perception of any situation depends only partly on sensory signals being received at that time.