I've just checked the BSP sources and indeed on the previous image you would have OTA partition cleared - good catch (I've moved off that one quite a while ago and haven't used OTA to do that). Home would be cleared as well,only /home/root would be preserved.
Now on ww42 image (current one in the Downloads section, you call it build_16), they've changed the boot target for the OTA case and it's now ota-update (which doesn't touch home and OTA partitions at all) instead of the first-install one (which should preserve only /home/root and reformats that partition + reformats the OTA partition).
You can check all of this by looking at the BSP sources, namely these files:
- edison-src/device-software/meta-edison-distro/recipes-core/first-install/files/first-install.sh
- edison-src/device-software/meta-edison-distro/recipes-core/ota-update/files/first-install.sh
- edison-src/device-software/utils/flash/ota_update.cmd (this is what becomes ota_update.scr during postBuild.sh run and then is executed during OTA)
So it's /home and the OTA partitions which aren't being cleared and the OTA partition is separate from all other ones (but is on the same MMC flash), so you can't corrupt it by just overfilling the rootfs with data, you'd need to mess up with fdisk or parted or write to the disk directly to accomplish that. Neither can OTA data corrupt the rootfs.