A customer-facing engineer is essentially an engineer who has people skills.
But remember, that for the purposes of these tutorials, a customer-facing engineer:
1) Must truly be an engineer; that is, he/she must work hands-on with technology and not just be an "overseer" of technical projects.
2) Must be interacting with customers consistently and forming deep relationships with them. This often means working with only a few "enterprise-level" customers at once, so a lot of attention can be given to each one.