Can Someone Explain How This Email Marketing Sequence Works?

Sound like a list swap
To grow their list or to make some money
People can mail out for other people

So the mail out another person offer in exchange for a similar reciprocal mailing
or they may sell it for cash

That has to be the most common reason someone, who already has you on there list
send you to an other squeeze page but there are other reasons
such as moving you through a sales funnel

In your case It was a swap or sale

It's hard to say without more information, but here are a couple of things that could be happening. And remember these are all just speculation.

Option #1
You are on (Person A's) main freebie list or even main buyers list, and by sending you to watch the video they could be segmenting their list to see who has a specific interest in the topic that video is on, and you will probably recieve more offers on that particular topic.

So in this case let's say their main list is on traffic generation which could cover topics like how to get traffic through facebook, twitter, articles, banners and PPC.

Then they send you to a free video on PPC. By having you opt-in you are basically telling them that you have an interest in PPC.

So they have just segmented you from the rest of their list, who could be people who don't have interest in PPC.

Because of this segmentation, they will now have you and a group of other people who are all interested in PPC. And knowing that they can send just you and that group offers on PPC.

Option #2
Another option is that when (Person A) sent you to that video, you might think it was from him, but it could actually be that you are going to end up on another persons list (Person C) who you don't know about yet.

Option #3
The worst case scenerio is that (Person A) has got you to opt-in for a list where you are going to be getting spammed like crazy.

Option #4
(Person B) could actually be the same person as (Person A) and just one of their aliases, unless you know that they are actually different people. There are some IMers who have multiple aliases that you think are different people but they are one and the same and they have you basically on more than one of their lists.

Option #5
It is possible that when you clicked on the link from (Person B) to watch (Person A's) video, that you clicked through an affiliate link. So if you did buy something then (Person B) would have gotten a commission.

Thanks Shane, the pity is (for them) that I was looking for whatever freebies Person A was going to give me, with no intention of buying his high end product that I knew would come after his second video at the end of his funnel.

And I opened Person B's email and followed the link to see if it was the same video, and work out what they were up to - in the fine tradition of Watch and Learn.... and only part with real money under exceptional circumstances.