Pentax didn't go after the pro market in the same way that Nikon, Canon and to a degree Olympus did.
Their cameras were intended for the consumer market. I'm sure that pros bought them, but that wasn't the primary market for Pentax.
The KX is an excellent camera. Its shutter might be a bit noisy but no more so than rival cameras sold during that same era.
Olympus (as it often did) started the downsizing trend with its OM-1, which was smaller, lighter and quieter than other cameras. Other makers followed suit: Pentax with the MX and ME cameras. Canon with the "A" series. Minolta with the "X" series. Nikon with its FM and FE models.
I wouldn't spend a lot of time worrying whether it was a pro or amateur camera. It's more important than the camera work correctly. And I wouldn't buy a camera from a newspaper photographer, as they tended to beat the daylights out of their gear.