Caught in the act

I must be making a mistake. Any suggestions/pointers as to where my analysis has gone wrong is welcome.

Here’s the gist of it. Clare reports she’s caught  Korean Air 129 En Route From Seoul To Auckland ‘in the act’ of laying down a ‘chemtrail’.

Anyway, following the Appleman Chart video guide that Clare has so helpfully been referring people to recently, I looked up the nearest upper atmosphere sounding (Whenupai) to get an idea of upper atmosphere conditions at the time. Now, ‘normal’ cruising altitudes for 747-400 can vary greatly, but let’s say for the sake of argument and erring on the side of conservatism, that it was somewhere in the bally-hoo of 25000 to 30000ft as it approached Auckland for landing. I got this…

So, here’s where I’m not sure. At the higher altitude (within normal 747-400 cruising range), it would seem that contrails were almost certain to occur, at the lower one (assuming some altitude drop on approach to Auckland), we’re in the ‘maybe’ range. But if that’s the case, why has Clare deemed her observation as a ‘chemtrail’ certainty when it goes against the advice of the guide she herself has been advising people to use when trying to determine what and what is not a ‘chemtrail’. Am I grossly over-estimating the altitude of a 747-400 that’s twenty minutes from its arrival time?

Can someone with a greater handle on the science in this situation steer me right? Thanks.

(I should point out, I’m not being entirely disingenuous here, I honestly think I must have made a mistake if Clare is so being so adamant about her observation).