I didn't know about this and it sounds interesting, so I've been trying to google how shortcodes can lead to theft as you describe and I think I just don't have the right terms for it because I'm getting results that match my terms but not the topic.
I think he was trying to say that phone theft can benefit the same way as credit card theft.
The thief uses the phone to buy stuff before the user reports it stolen.
In this case the stuff that is bought is mobile services that are billed for example 100€ for each SMS message. The victims mobile subscription plan gets the bill and the associates of the thief get the money.
Any chance you'd have article links?