sadly, most people here have no actual idea about how tornado works, since they have never mained voyager in a PK.
anyway, the only thing that could justify this behaviour ingame is the following thing happening (which im sure you experienced before with slashes):
lets say you and another voyager were just close enough so you could see him from your screen but he was almost out of it. a character enters by the other voyager's side, and he tornadoes it and disappear from your screen. that char stays flying. you try to tornado the char that enters your side of the screen but since he was very far from your click, you end up missing the tornado but the animation gets bugged telling you you asserted it. however once the character gets back to you, since you already had a tornado animation by your screen, that character in which it missed might actually get the animation if it gets bugged by the other char still flying (both chars must be in the very edges of your screen vision).
this is a very common bug when youre a crusader. it happens sometimes when you try to slash an enemy and randomly end up slashing a guildmate even though you never clicked him. heres one of my videos showing how this bug works: (from minute 14:13 to 14:21)
(i am very sorry about having to link it here, please do not delete, it only has the purpose of showing how the bug works)
this small part of the video shows me clicking on Lua# and him running out the edge of my screen vision, then my click going to EZ9 even though i never even clicked him at all and leading me to die.
ive seen characters being sealed and still being able to attack me. ive always related this bug to it, since it applies to most of the cases.
this is all i could think of. this is however veeeery unlikely to happen... but it could happen.