I think you forgot to add some important information in your OP, one factor to be considered is that Russian local board was the first local board on bitcointalk. Which means they have been around for the longest time, and also considering their affinity for speaking their own language in IRL and on every online platform. Other local boards That alone is enough reason for their local board to be more active over the years than the others in the forum.
There isn't strong evidence to prove Satoshi's a Russian. How do you know the first local board was Russian?
This has made me think that Satoshi is a Russian.
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This is a wrong conclusion. The forum activity you have shown refers only to local boards and doesn't include the main forum boards. Do you know how many Americans are active on the forums? Or British, Canadian and Australian members—how many of them post here regularly? Besides, Russia is a very large country with a larger population than many western nations. Have you ever considered that maybe the Russian local board is so active because English isn't as prevalent among Russians? Russians tend to use their native language and the Cyrillic alphabet. Many Russians also speak other languages, but students can choose from different language such as German or French—not necessarily English.
His conclusion's wrong. It's based on his opinion. He's finding something to connect together to make the wrong conclusion. Satoshi had clean GB English & international English, there isn't strong evidence supporting Satoshi was Russian. There's evidence Satoshi's a pseudonym used by more than one person.
So you're guessing Satoshi is a Russian because Russian board has a lot post and active members among other local board in this forum?
If I create 300 alt accounts and then make 3000 post on Turkish board, would you say Satoshi is from Turkish? If I create 400 alt accounts and then make 6000 post on new local board e.g. Nepal, would you say Satoshi is from Nepal?
Your assumption isn't make sense and there's 0% correlation about it.
He doesn't see there's 0% correlation or his assumption isn't making sense, he's convinced.