Yes, those holes in the background are the result of star removal and replacement with smaller stars. I used starnet++ for the first time to remove stars and I think it's great. It does leave artifacts though. I could spend some more time using Photoshop's heal function. I eliminated almost all artifacts off the nebula area but with >9000 stars in the uncropped image (according the the PSF tool in PixInsight), it's a big job to get them all with this dense star field.
Azure vase sponge sounds good! Maybe even those ancient containers for hauling wine in (without the handles).
The deal is there are very few images of this planetary and I think they all don't show dust, just gaps in the nebula that make you think the nebula explosion was at least partially asymmetric. But from what I see in this image, it looks completely symmetric and mostly intact (on one side anyway). Its just partially obscured in dust which is maybe something new. Or... maybe not, if I'm not seeing straight.