flattened

flattenは「〈地面などを〉平らにする」や「…を単調にする」（『プログレッシブ英和中辞典』小学館）という意味の動詞ですが，ここでは「（発音を）簡略化する」あるいは「なまる」という意味で用いられていると考えられます。よって本文のAdrian becomes flattened into alien.は「Adrianがなまってalienに聞こえる」と解釈できるのではないでしょうか。（Koyamamoto）

British photographer documents lives outside the lines
Nomadic Adrian 'Uchujin' Storey opens up new worlds by focusing on lesser-told tales
Uchujin, aka Adrian Storey, a British photographer and filmmaker based in Tokyo, drolly explains his rather unusual business moniker: “I’d rather be an alien than an outsider.” Although usually translated simply as “alien,” “uchujin” has a universe of meaning in his storytelling world.
... Storey took the name Uchujin when he became serious about photography — even before he came to Japan. “When I was living in Thailand, there is also a pronunciation issue with r’s and l’s like in most of Asia, so many people could not pronounce my name well. Adrian becomes flattened into alien. And I quite liked the nickname ‘alien,’ because in China you get an alien’s permit and in Japan, the alien registration card, and I much preferred alien to ‘foreigner’ especially in a country like India, where you really feel like an alien, like you’ve stumbled upon another planet.”
http://www.japantimes.co.jp/community/2013/02/15/our-lives/british-photographer-documents-people-who-live-outside-the-norm/#.USInJY7QVqM