I read that kettlebells training does not isolate the muscles, contrary to dumbbell or dead-lifts. What does this mean to the effects in the body? If you look at someone and try to guess how he was training, would you be able to see it?
Your original statement is not correct. Deadlifts are compound exercises that, when completed, activate a large group of muscles .
- The grip strength (finger flexors) and the lower back (erector spinae) work isometrically to keep the bar held in the hands and to keep the spine from rounding.
- The gluteus maximus and hamstrings work to extend the hip joint.
- The quadriceps work to extend the knee joint.
- The adductor magnus works to stabilize the legs.
It is extremely hard to guess how someone is training by their physique. If you assumed that all people train in a *optimal way then you could say that of people lifting weights, newbies are aiming for compound exercises with no isolation. Intermediates are working on a mix of compound and isolation and advanced are working mostly isolation.
This, in practice does not work as a estimation method. For evidence, go to a gym and ask around.
(* optimal according to source )
 Mark Rippetoe with Lon Kilgore, Starting Strength, The Aasgaard Company Publishers, 2005, ISBN 0-9768054-0-5