QSDK is based on OpenWRT 15.05, but it’s changed enough that it really cannot be consider OpenWRT…
QSDK keeps current for many of the FOSS packages, and integrates their items as needed to support the reference boards they have designed and released - MESH is one of those items, along with 802.11ac Wave2, and QSDK also includes the network acceleration stuff for cut-thru forwarding (speaking broadly) - some of this work does end up back on OpenWRT master as commits if the code contributed is GPLv2 compatible.