One paragraph in Chapter 10 of Reign Of Shadows lists all the characters sent into space, and Lewa wasn’t amongst them.
That paragraph in Chapter 11 was only published after the error was pointed out; the above question was asked in between the two chapters, as evidenced by the rest of the discussion:
Admittedly, it’s possible that Greg had always intended to have Teridax attempt to leave Lewa behind, and Lewa’s omission was coincidental and unrelated, but this, to me, reads as if the start of Chapter 11 was written to fix the previous error.