It’s not inconceivable that it was on those chat logs alone. In the us the jury instructions read something to the effect of “this is what beyond a reasonable doubt means. It is up to you to determine if the prosecution has met that burden and you choose to apply as much or little weight to any piece of evidence or testimony as you see fit”

They had the victim's device and logs from the messaging service. The issue was that the logs were attributed to the wrong user.

There's a lot missing in this article. Obvious follow-up questions unanswered.