They're probably (almost definitely) both automated emails. The point is that they're a bit better than "Hi. Click this link. Buy some more stuff from us."

It all sounds very nice, but unless you have professional tech support, this will not scale. Imagine your registrations grow 100X - you will drown yourself in email requests.

It doesn't matter -- you SHOULD be doing things at the beginning of your startup that does not scale.

The fact of the matter is that it is extremely unlikely that you will ever get 100X registrations -- it just does not happen. Most people "launch" a landing page or their MVP, and it's more of a squeak than a bang.

You need to make your early customers evangelicals, and you do that by doing things for them that do not scale. Something cool like the Skills welcome email is very appropriate, and if executed sincerely, does a great job to convert casual surfers to potential users.