I think witnesses (across the board) could be more articulate in their responses - but they are just human and they also are aware they are being cross-examined by someone who is not for them... and in some cases is trying to lead a jury to think they are a murderer or involved in a murder conspiracy. Again, they are just humans.
But, try it like this... getting on a treadmill does not make one a "runner." Doing a bench press does not make one a "weight lifter." Playing pick up basketball in the park does not make one a "basketball player."
In my younger days, among various things I'd do at the gym, I would punch a bag from time to time and even simulate rounds of boxing. I never had a single minute of formal training, never fought anyone in a ring or elsewhere, and never in my life have I told anyone I'm a "boxer" or that I "box."