It is inconclusive to say 1/3 of the angels fell. We read in
Rev 12 that 1/3 of the stars were thrown down by the dragon's tail, but we are not told WHEN that occurred, neither are we told they are heavenly angels. Just stars. Stars in
Rev 1 were angels of the churches.
But we do read that angels lost their first estate. That can only mean they have free will. We do not know WHEN they fell or WHY. Jude only mentioned they did. And that implies lack of faithfulness.
Jude 1:6 KJV And the angels which kept not their first estate, but left their own habitation, he hath reserved in everlasting chains under darkness unto the judgment of the great day.
Tradition alone says 1/3 of the stars falling means heavenly angels. It is only conjecture.