nano changed to GPLv3 7 years ago (see commit in URL), but meta-oe still uses GPLv2 as LICENSE. LIC_FILES_CHKSUM was updated, but LICENSE field wasn't adjusted.
The nano recipe is in meta-oe as you've noted, and I'm afraid the Yocto Project doesn't generally maintain recipes in that layer. In general issues with meta-oe should be reported to the openembedded-devel@lists.openembedded.org mailing list so that someone there can look into it. This does look like something that should be corrected fairly swiftly though.