I'm not sure his native language is english; he may be swedish.
Also, regarding his writing, he did at least preface his post with This is a brain-dump-stream-of-consciousness-thing. Despite being a stickler for grammar rules myself, if I don't proofread my writing, there are bound to be plenty of grammar errors and typos that pop up, especially if my brain is really flying with ideas and my fingers are struggling to keep up. His post had that feel to it as well. A bunch of ideas, semi-related, bouncing ideas around haphazardly.
He showed us his early design documents of erlang, including original compile times and performance measurements. Awesome stuff.
He does sound British, but there's a certain foreign-ness about the way he speaks (probably picked up from Ericsson).
Source 1: My opinion. I've met him many times.
Source 2: His thesis states that he started at the Ericsson CSLab in 1985. CSLab was in Sweden.
Source 3: This (http://www.cse.chalmers.se/~rjmh/Armstrong/bits.ps) set of slides states that he has a B.Sc. from UCL (London) from 1972 and started at CSLAb in 1986 (not 1985, seems the dates are a bit fluid).