That tweet makes me think of Simon's second conversation with Catherine. (Incidentally, Catherine's nonchalant manner is really creepy. Also, a "grimoire" is a book of magic spells.)
Spoiler below!
Simon: Hey, are you there? I found the domed ceiling. Catherine: Oh, that's better. Simon, was it? Simon: Jarrett. Simon Jarrett. Catherine: Hi, Simon. I'm Catherine. Have you figured out what's going on yet? Simon: Me? I was hoping you'd have some answers. Catherine: I probably have some. What do you want to know? Simon: Where to even begin? I mean, what is this place? How did I get here? And why do the robots talk like they're people? Catherine: Well, you're at Upsilon, clearly. Have you never been there before? Where do you work? Simon: The Grimoire, in Toronto. Is that really important? Catherine: No, I mean, where did you work in PATHOS-2? Simon: I don't know what that is! Catherine: That's unexpected. Did you come directly from Toronto? Simon: Yes, and it was very unexpected! Catherine: Have you seen any people? Like staff or field technicians? Simon: Only robots. Crazy ones. Catherine: This is all so strange. Simon: You're telling me... what was that? No! Catherine: What's going on? Simon: I think this place is about to collapse! What do I do? Catherine: Simon, come to Lambda! Simon: How - how do I get there? Catherine: There are several trains connecting all the sites! Find one and come here! I'll wait for you!
So Simon has never even heard of PATHOS-2, which is odd, given that its construction was probably high-profile. He doesn't seem to know about the asteroid strike either. My guess is that he came from a time period predating both of those events (circa 2015, perhaps), before waking up and finding himself in PATHOS-2.
This fits with the idea that horror is most effective when it's close to home. If it could happen to Simon, it could happen to you, the player. Hence the "brainfuck" tweet and the requirement that previews omit the start of the game. The question is, how could Simon suddenly end up in PATHOS-2, many miles and years away?
Here's my theory. In the E3 trailer, we briefly see Simon in some sort of rotating brain scanner. This occurs at the start of the game. Simon volunteers to have his brain scanned, either for scientific research or as an attempt to prolong his life via a digital backup copy (analogous to current attempts using cryogenics).
At this point, Simon's consciousness "forks". One version of himself steps out of the scanner and leads a normal life, until the asteroid strike kills him along with everyone else. The other version, containing all of his memories up until the moment he leaves the scanner, exists in storage until PATHOS-2 somehow retrieves the data and recreates him.
From "new Simon's" perspective, he instantly jumps from the scanner to PATHOS-2. It's not clear how he's recreated, though. Is he inhabiting a different body, with his mind contained in one of those spiky metal objects from the teaser? Or is he a robot, an android, or a digital simulation? What do you think?