Yes, it probably is. Right, they use many email addresses (and variations with extensions like, right now, vip852+e9v01a@gmail.com). But they use one email address for hundreds of instances in parallel. And for instances that use our shared mail infrastructure, mxout.saasweb.net (sorry, not yours), we see these confirmation emails all coming in in parallel. The first three get through, but thereafter, we just drop the rest. This should leave the registrations in their unconfirmed state (and auto-deleted after 7 days) for most of the instances, at least.
So no silver bullet to solve this spam wave…
We do that primarily to keep email reputation high and our out queue small. Hundreds of these confirmation emails sit in our out queue right now because Gmail rate-limits their incoming emails. ("The user you are trying to contact is receiving mail at a rate that prevents additional messages from being delivered.")