That is just one example of the use of an omniscient narrator
in the NT. It is used quite often in literature and we modern people who are used to reading novels that use that device think nothing of it. But it is a big problem if you want to claim the gospels are eye witness accounts.
Just staying within Matt26, the chapter with Gethsememe, we have several examples. 26:3-5 Then the chief priests and the elders of the people gathered in the palace of the high priest, who was called Caiaphas, 4 and they conspired to arrest Jesus by stealth and kill him. 5 But they said, “Not during the festival, or there may be a riot among the people.”
How would the writer of Matt know that?26:14-15 14 Then one of the twelve, who was called Judas Iscariot, went to the chief priests 15 and said, “What will you give me if I betray him to you?” They paid him thirty pieces of silver.
How would the writer of Matt know that?26:48 Now the betrayer had given them a sign, saying, “The one I will kiss is the man; arrest him.”
How would the writer of Matt know that? A true eye witness may not have even known Judas had betrayed him and certainly would not have know there was a signal.
In 26:58 it seems as if the writer was aware he needed a witness so he had Peter follow the captive jesus H all the way to the courtyard of the high priests. Does it seem odd that he would be able to infiltrate so far into their HQ so as to be able to hear their plotting?
This kind of problem is all over the NT and even the OT. Moses' funeral is described in a story supposedly written by moses. And which apostle was it that witnessed satan tempting jesus H?
It's amusing that the in the link MM provided, they ignorantly call it a "know it all narrator". Morons. They also try to say that the fact that Matt is so obviously flawed is a reason to think it is legitimate. Yeah, good answer. If a bad writer is the mark of authenticity, then Interview with a Vampire must also be a documentary.