Yikes. I often wonder about this when booking my own awards on the phone - the questions they ask just aren't that hard to get. Half the time all they want is my home address - where I live, if you own your own house, that's public record!
In this case, one would hope that the friend would have told you they were making such a change before trying it. I'd certainly expect my friends/family to do that if I bought them a plane ticket.
To be fair though, I can actually see a situation where a) they didn't want to bother you after already receiving your generosity and b) on the phone, 117k and 170k can sound very, very similar. Not too far of a stretch to hear a DL rep say something like: "The old ticket cost ahundredseventeen thousand miles. The new ticket prices out at ahundredseventy thousand and you have to pay a $150 change fee" and the friend thinking "oh cool, sounds like the same price and I'll just pay that $150".