I added some context through the links at the bottom of the map: you can go to http://migrationsmap.net/about.html or directly to the page where the data is coming from: http://www.migrationdrc.org/research/typesofmigration/global...
It's also confusing in that the number format follows a European convention of using decimal points rather than commas in between every three digits the numbers, though I can accept that localising your site isn't a big concern.