Yeah that's right. "Capter quelqu'un dans la rue" means "saluer quelqu'un", meet someone. This quotation means that some people add a lot of "friends" on facebook but they are not real friends because they don't pay any attention for you in the real life.
[…] To answer your question, one cannot say that « 'capter' has replaced 'saluer'/'reconnaître' in informal French ». Not for the general public anyway. I suspect that it is used here specifically as a pun to emphasize the paradoxical situation which Missiou has explained. Facebook users ‘captent’ radio signals (which is one of the basic meanings of the word) but not visual contact ; they are friends only when using fashionable media.
So, don’t worry, in everyday life, you can still use 'saluer'/'reconnaître'.