I was going through George's Purrfect Ai tutorials and whilst looking at his ai4 code I found this called in the enemy action:

find_path(my.start_node, target_node, my.skill48, path_index)

my.startnode is the enemies closest node already defined.
my.skill48 is the enemy ID which also is already defined.

Now my problem is that Ive made a function that is called by one of my enemies and I found that I dont need to pass its ID number across (eg, my.skill48) for it to work on that particular enemy. The function still seems to retain the "my." pointer for the calling entity and Ive got six enemies calling the same function and working.

Am I just being dumb or is this something unique to the C-script compiler?

No you're not dumb.
Every function called by an entity has its own my pointer set to that very entity.
If an amount of x entities call the same function you have a number of x function instances running. Each with a different my pointer, pointing to the entity which called the function.