WordPress displays its version number and file path in your homepage as the Generator. This scanner visits your homepage and checks for the generator tag. The WordPress core team has decided that displaying your WordPress version to the public is not a security concern.
Installing security updates is important and I hope that a big red message would help encourage people to update WordPress more often. I'm also hopeful that the WordPress core team will decide to stop displaying version numbers.
Almost everyone who uses this scanner is not running their updates.