Hello, PKing admin here.
So, you were PKed because you left the faction. When joining factions, you get a prompt on your screen asking you to agree to take the risks of being a criminal, and one of those risks is being PKed.
As Falcon showed, you purchased their illegal product, and by buying that product that makes you a problem for the faction if you leave, you've seen their illegal side which makes you a criminal, NOT "(Security, waiters, doormen, drivers, etc)". If you read the PK guidelines "This 'left faction' reason is valid for 2 weeks after the individual leaves" and they placed the orders within hours of you leaving.