True. A negative event could serve as a catalyst for change and external incentives can get the ball rolling but I hope he doesn't reenact a Rocky sequence with the "Eye of the Tiger" playing in the background visualizing a revenge body to get back at this random girl that he'll likely never see again.Self-betterment is largely driven by outside incentive. He should definitely use it as motivation, but from the right people. Some random Xalimo getting picked up outside is not someone you should model yourself to.
I agree with the second part, that's one thing I'll never understand. Trying to pick up literal random girls in a shopping centre. Afaik that concept literally doesn't exist in Europe outside of maybe London. If there's no excuse for you to interact with her like on the train - you're going to come off as creepy most of the time. Even if I were to succeed, I'd be suspicious of the quality of what exactly I picked up.
For myself any sustained life change has often been precipitated not by self-doubt or feelings of insecurity (though I could see this as working to get one moving). For instance, going to the gym wouldn't be to quell feelings of inadequacy (from but one encounter) but from the benefits accrued from feeling better than one's baseline. It's just a thought. Sure there are obviously external rewards like positive feedback, increased feelings of self-assuredness, increased levels of physical attractiveness and so forth.
It's kind of amusing that he approached because she was Somali assuming he'd have an easier time at linking up but it blew up in his face. We often assume random passersby that engage with us without reason are a little batty.