vBSEO - site activity vs Alexa Ranking

[YabbaDabba]

This is a slight twist on the standard :up::down: discussion of vBSEO.

I thought I would look at how well vBSEO had worked on the vBSEO site.

At first glance I was impressed. For not much content, I see a rank of about 10,000. Wow, I thought.

However, as I look at the Alexa history for them, I see their historical rank drifting down to under 100,000 during the last 2 years. (Given their thin content, this is what I had more-or-less expected.)

But SUDDENLY at the end of March a swift leap up the ranks to the 10,000 range.

So, my question is this: What happened on the vBSEO site that may have caused this?

I almost never go there, so I don't know what happened. I'm hoping some of you here who frequent their site may know.

Thanks in advance.