I really don't know, but I doubt it. In the first place, AFAIK the ELB joint has always been referred to as having a spot weld. I can't remember a question about using solder having ever come up before. I'm still using ELB's that I got with the original Cloud and I've only had one come apart. If the ELB bonds were made with just a traditional soft lead solder, they would have certainly broken down by now.
Secondly and more definitively, given current prohibitive regulations in the U.S. and EU, consumer electronics manufacturers having moved to lead-free solder decades ago, and even high-heat soft solders (~600-800F melting point) only being used in specialized applications, it seems extremely unlikely (if not illegal) that an inappropriate solder would be used in the ELB's.
That's just my
. If you are seriously concerned, you can contact VXL Support (although this question may need to be fielded by Seibo himself).