The viewer is seeing what Bale is reading in a diary...a diary that he is being lied to in...
the movie is being shown from the perspective of that diary
That is why Cutter says in the end , "You won't find the secret. You want to be fooled." So keep that in mind and then the movie is really a 2 hour long simple magic show, intended to trick its viewers, and that's exactly what it does!.
If Bordon knew about Tesla and his machine( which he did as in his diary), why would he be intent to give that information to his number one rival Angier, as his diary was specifically intended to be read by Angier. So why would Bordon be still surprised as to how Angier performs the "Real Transported Man" trick? . Borden clearly knew who Nikola Tesla was and what he could and could not do. Tesla tried to explain Angier and fooled Angier, He pulled the wool over Angier's eyes with the cat and the top hat, WHO CANT FIND MULTIPLE BLACK HATS AND CATS. Angier fell right into his trick, gave him money, Tesla left a piece of shyt and Angier realized the key to a good trick is taking the real secret to the grave.
The point of this film is the whole movie was a magic trick. We were tricked into believing the machine actually worked. This movie is not "Science Fiction Movie", ......So why would they suddenly spring science fiction on us. They didn't, we were tricked into believing it was a working cloning machine. This movie is "Mystery, Thriller, Drama".
Cutter also said early into the film POINT BLANK that it's real! That scene wasn't a flashback. It wasn't from Angier's or either of the Bolden twin's perspective. It was in that PRESENT TIME.
In fact, I already posted the interview of Johnathan Nolan who WROTE the screenplay stating that they wanted the people watching the film know off the bat.
End of discussion.
EDIT. I'll answer your questions because you clearly never paid attention of this movie AT ALL.
1.) Borden DID NOT know about the transporter machine. Never mind the diary part where he merely stated that "Tesla" was only the keyword to decode his diary. But the reason he gave Angier his diary was to send him off on a wild goose clear out in the United States far away from London! He did not know Tesla was capable of building such a machine. He never met the man at all.
Answer yourself this question, if that was the so-called case, why did the Borden twins, especially Fredrick, got so upset over not figuring out how Angier was transporting himself after he returned from the States? If he knew he went to Telsa to build a fake transporter machine, then obviously he would of known the trick and manipulate it once again like he did the last several times.
2.) You do know the actual history between Telsa and Edison, correct? You did see that Edison's men was hanging around the hotel, did you not? You saw them burning down the entire establishment that Telsa was residing at? And you actually assume that Telsa dipped out of town because he was scamming Angier? What evidence do you even have to support this? Or any of it?
And lastly, 3.) It is INDEED a science fiction picture. Who ever told you that it was not? Again, I refer to you back to the Johnathan Nolan interview that specifically stated they intended to put the supernatural into the picture. The only reason you made this illogical analysis of the film up is because you refuse to believe that is a science fiction feature set in a period era.