Probably a tiny fraction. I'd guess that an algorithm recognized that buying 100 Bitcoin spread across 100k accounts is better than from 1 account.

You need ID verification to trade on the account, I dont think you can make 100s of accounts for one trader

That's interesting. I thought the Bitcoin folks were all about anonymity.

Do orderbooks display account information? AFAIK 1 person putting 1000 orders and 1000 people each putting in 1 order looks identical (unless you're the exchange operator)

Not sure. This is somewhat the motivation for "dark pools" in the regular equities markets.