Players cannot upload their models to the server.
Those 2 people were telling the truth.
If you replace a default model with a custom model on your game directory than it only applies to you and only you.
You need to hand-pick and manually upload the models
sv_allowupload "1" allows you to use your custom spray on public servers.
Browse sprays here
https://gamebanana.com/sprays/cats/610
Spray is you press T on your keyboard near a wall, a typical old school player sprays every time he gets a kill, an old habit.
To find description of any cvar follow this link
http://txdv.github.io/cstrike-cvarlist/