I'm not sure about what OP was thinking, but I felt the same way. The article seemed to have mixed messages. One was, "how dare you steal from us" and the other was "Everyone steals".
Looking at the two sites, they were both using such common web design styles these days, that I would have assumed they both based their site off of someone else's.
If I were them, I would have stuck to the second argument, realized that no idea or design is a unique snowflake and everyone steals constantly.
"But after some thought, Darko, our design lead (he's a very nice person) convinced me to give you guys the benefit of the doubt and not send the Croatian emmigration in Australia (known for working as bouncers and construction workers) knocking at your door."
Yeah. You tend to lose the moral initiative when you pretend you have the backing of some nefarious street thugs.
I think he's referring to how they are arrogant for threatening them, sending them "design tips", and playing themselves up as sexy and dangerous all in the same message.
They definitely have a valid point about the plagiarism but they're being really cocky and showy about it.
Edit: Ya, they might have been trying to be funny or venting, I can understand that. But they really shouldn't have ANY kind of physical threat in there at all. Its childish and just pointless posturing.
Are you saying they are arrogant for outing a plagiarizer?