I'm going to text my friend about a passenger on my flight
Why would you want to text your friend about this random passenger?
Yes, do you mind me texting him about it?
I understand that you want to tell your friend what is going on around you. But is rude to talk about someone behind their back by texting about them.
It shouldn't be wrong to talk about things.
It depends on how you speak about this person. Speaking poorly behind their back is just rude. If you have something nice to say about them however, I'm sure they wouldn't mind too much to be spoken about.