In theory it would, but the practical answer is that for non-English-language community in 2010 migration to Reddit could not have happened.
The community in question was Russian, so it migrated not to FB, but to VK, which is essentially the same. It did not migrate there because members found VK to be a better platform for their community though - they just started using VK to communicate with their peers, were spending their time there and gradually stopped visiting forums.
Reddit never gained much traction in Russia, and in 2010-2012 it was for the nerdiest of nerds. One was way more likely to frequently visit some forum than Reddit back then.
The community in question was Russian, so it migrated not to FB, but to VK, which is essentially the same. It did not migrate there because members found VK to be a better platform for their community though - they just started using VK to communicate with their peers, were spending their time there and gradually stopped visiting forums.
Reddit never gained much traction in Russia, and in 2010-2012 it was for the nerdiest of nerds. One was way more likely to frequently visit some forum than Reddit back then.