In-Game Events and Gatherings

I have some questions regarding implants that are received from the new Serpents event. Yesterday I got really lucky and received three of them as drops and it was the first time I’ve ever received any despite running maybe 50 sites.
Do you guys know what causes them to drop from the sites? Is there any way to tell by the site name or the way it looks? Does security status matter?

All three of the drops I’ve received where in highsec at .5 security space. During each drop I noticed that angel cartel reinforcements came to help so I’m not sure if that has something to do with it. For two of the sites cruisers came and I received two mid-grade implants (one from each site). For the third site battlecruisers came and for that one I received a high-grade implant. It kind of seems like enemy reinforcements might be a predictor of what’s in the container and the type of ship that warps in might indicate that as well.

Sorry if all of this is on a dev blog somewhere. I looked through them but all they mentioned was that the implants drop from special sites and that was it.