angbucu on "[Plugin: WordPress SEO by Yoast] Old post reposted without instruction - is this SEO"

I'm really not familiar with SEO but have your plugin and am blundering my way around it. However today I had an old post from 1 month ago repost. I didn't republish or do anything for that matter in WO backend to cause this to happen. Searching for solutions online I got one hit that suggest that this may be SEO. Is this caused by SEO or the plugin?
thanks

http://wordpress.org/extend/plugins/wordpress-seo/