Skepticism always welcome. I like your train of thought, but the argument is still lacking. My argument against your idea so far is that:

[1] As a natural speaker of English, the IRC conversation looks *very* legitimate. The back and forth looks like it is genuinely two separate people (opinion only)
[2] If sango doesn't compensate the loss to his clients, will his business survive? Will the bad reputation caused by this incident kill the business? Is it worth to kill the business for 511BTC?
[3] As per defxor, Occam's razor would place the burden on you to convince otherwise. Until then, simplest explanation to fit with facts will be most believable. Maybe search for some more facts and you can make your claim seem more persuasive.