Discussion❓ shooting throug thin walls

Hello Everyone ,
so basically a week ago on prophunt server
I saw someone he claims he was using A I M W A R E hacks

so when I was blocking the door he was using his shotgun (he was also spinbotting) and hitting the door many times till it suddenly hit me

if someone else would try a 1000 hit on the door it wouldn't hit me

thought when I go outside the map , he couldn't hit me ,so obv he dose not have rcon access

Anyone knows what's the advantages called and how he could do it ?

The default HL2 weapons can't shoot through walls. Once the bullet trace hits something it stops.