So instead of being on first, he should have gotten second then I guess by reading that. Thanks for the clarification.
Based on the latest update, this is very accurate.
Rule 7.01 (see above for link) states that
Rule 7.01 Comment: If a runner legally acquires title to a base, and the pitcher assumes his pitching position, the runner may not return to a previously occupied base.
Which the update article states should be interpreted as: Segura shouldn't have been allowed to go back to first, specifically because Segura was on second when the play started. Therefore, at the end of the play, Segura isn't entitled to first base.
One could also argue that the comments about Segura being out of the baseline are accurate, given that he shouldn't have been allowed to go back to first.
This all assumes that the new article has the correct rules interpretation. MLB hasn't stated their official position yet.