Can Thrash detain Iso while in his ult ?

I just played a swiftplay where I my teammate got Iso ulted, I sent Thrash after another enemy and when I jumped on the enemy I think I was very close to where Iso's purple spawn mark was on the floor.

Next round, the recap tells me I detained 2 people even though I used ult only once, when there were two enemies left and I did detain one of them but the other was Iso in his ult.

And my teammate won the duel but they were top frag so I don't know if my ult did help or if it's just that they won on their own.

I guess I should test in a custom game with a couple friends but I don't have any.