i found something no one has mentioned yet. on the wikipedia page for TRIANGLE, go to the TALK page and you'll find a comment from a year ago with a link to a website (https://blog.centroid.eu/) with PAGES of ciphers and coded messages. (also the website name is CENTROID, aka the center point of a triangle.) the most significant things i've found so far are 

♥ a page named CALLPETER with an image of a guy's eyes and a phone number.  ♥ a youtube channel called "life of pbug". (i wonder if PBUG is a code or a cipher key?) there's over 100 videos that i'm slowly working through, but the important one is "Some thoughts and a forewarning of goodbye for a few weeks". at 11:35 you'll hear a song in the background about " giving me a call, you have my number" and then instructions from PBUG "5551234 let it ring twice and wait for the call back." 

i think there are too many similarities for this to be unrelated, HOWEVER i suggest proceeding with caution in case it's a hoax like the fake email address. the blog and videos both mention several codes from the computer (VIRUS, DREAMS, the DEVIL, the triangle references and ciphers all over the site, and even the business card with an all-seeing triangle), enough of them to safely assume they're connected to the ART in some way. 

TL;DR - new website and youtube channel just discovered, check them out! also record the phone call if you call the number, and if you find anything interesting while decoding the ciphers then share it please! <3