Some packages will show up as being in both AUR and Manjaro repo.
This is because the AUR package has been deemed so useful it has been included in Manjaro repo.
If such package as timeshift get’s enough votes to get into the official Arch repo then it will most like be removed from the Manjaro overlay to Arch repo.
You may also see a version mismatch between AUR and Manjaro because packages are rebuilt against unstable and enter in unstable - thus they will take the tour-de-branches before arriving in stable.