It seems like the author logged in to his seller account from a public wireless network (coffee shop, office) where another, previously-banned seller account had logged in from at one time, and Amazon assumed both accounts were from the same guy. Maybe they sold the same type of products.
I'm sure they get a lot of sellers who get their account closed and just try to make a new one, but I'd rather have Amazon not catch the sellers who are dumb enough to create an account from the same IP than catch them and get legitimate sellers banned in the process.
"Static IP addresses may be required or dynamic IP addresses may be assigned without a static IP request, depending on location."
I don't take notice of my IP address much, so I can't say if they assigned a static IP address in my case. If they're filtering on IP addresses, I imagine that they get a lot of false positives.
I'm sure there's a simpler explanation, though. That seems fairly complex.