I think the sense is more they're both about hundreds of unique physical characteristics, some of which are perhaps unquantifiable.
The shape of an instrument, the material used, the type of strings, their tension, the temperature and humidity in the room. The way each player holds it, the size of their hands, the specific strength of their fingers. Some of these factors stay constant, others change from day to day or player to player. The sum of all of these together creates a specific timbre.
The shape of an instrument, the material used, the type of strings, their tension, the temperature and humidity in the room. The way each player holds it, the size of their hands, the specific strength of their fingers. Some of these factors stay constant, others change from day to day or player to player. The sum of all of these together creates a specific timbre.