Interesting. Sounds like either he omitted part of the order (it's a single "item" so it shouldn't have shipped without the Anderson plug and boots) or perhaps you are mistaken on what you ordered and possibly ordered the bare brackets?
I'd double check your order, and if it's the former case, just email him accordingly with the facts and ask to be made whole (return/refund or send out missing parts).
Maybe that's already what you did and he hasn't responded in weeks or months? I'm not here to defend that.
Seems pretty easy on paper but the world's a complicated place with complicated people.
Boy you're really stretching to blame the customer.