Between plothole and time paradox...
The original turtles had:
1.Seen Splinter betrayed
2.Seen Earth destroyed
3.Been rescued by Fugitoid simultaneously with Earth's destruction
The "new" turtles haven't and...
4.They have heard how Fugitoid is not betraying them but sacrificing himself
5.Been told to trust Fugitoid.
6.Seen earth survive in a last stand by working with their own "original" turtles
And do not let me being about what "surviving" Fugitoid knows...
How will the timeline return to what it has been shown in this episode when every episode we have seen so far require the turtles to be unaware of this current development?
Just to show one such example:
The turtles yell at Splinter just before Shredder is to betray him, and Splinter is quick enough to act on this warning and change his own fate... The "new" turtles are unaware that fate would have fallen upon Splinter without the action of their future selves...
See it? This is just one point to consider, there are many more.