He's also fairly inconsistent. He occasionally uses -ize endings, e.g. "realize". He also uses some language that is more prevalent in North American English, e.g. "sucks", "gotten", "chump change" and others.
Someone attempting to use British English to obscure their identity would know to use words like "maths" and "flat", as he did; not as many people however are aware that British English doesn't (typically) feature the word "gotten", which he used on multiple occasions. To me, this lends to the theory the BrE was a misdirection.
(As an aside, he's inconsistent in some other things, like "e-mail" versus "email", "TOR" versus "Tor", and "double click" versus "doubleclick".)