Earlier quoted context omitted.
Funny enough, a similar thing (using obscure, ten-dollar words instead of simple ones) happens with many Russians learning English. It happens for a totally different reason - obviously Russian is a Slavic, not Romance language. Turns out that most high quality translated material for Russian is old literature and scientific papers. So that’s what the translators are trained on, and that’s what many Russians speaking…
I have witnessed this phenomenon living in London as a native of the city. A new-to-London Russian colleague of mine used ornate phraseology and what I would consider as 'posh' words quite regularly. A major phrase for her was "It seems to me" as a precursor to saying virtually any opinion. I never knew the reason for it though, so TIL.
He'd watched the series in German and then in English and knew it well enough to pick things up.
To my ear, his English was pretty good.
That said, the 2 groups of non-native speakers that have impressed me the most are people from Sweden and Norway. I've mistaken more than one of them for native speakers (to their delight) :D