While there is a lot of blurring between the terms, I believe there are visual differences that would warrant not aliasing one to the other. For a quilt, I believe it's most common to expect patchworking (ex: post #4725670, post #4338586) while for a comforter it would either be no pattern or typical fabric patterns (post #5306945, post #4127609).
Amongst both tags there are also posts that while there is the impression of thickness to imply it's not like a normal blanket, they lack any indications of quilting (the block or lines throughout). Ex: post #3774475, post #1849067, post #3561725. A lot of these appear to be kakebuton, which the wiki article calls a duvet. Although because of blurring terms and appearances, that also isn't very helpful based on wikipedia's article on it.
My suggestion though would be that quilt be reserved for patchwork types and comforter be used for the thick unpatterned and non-patchwork print (regardless of the presence of quilting) types.
General reading though at least in the differences between blanket, quilt, comforter, and duvet is that in terms of thickness (fluffiness?) blank < quilt < comforter <= duvet. Quilts, Comforters, and Duvets are made with three layers (bottom, middle filler, and top) while a blanket is a single layer. Quilts frequently feature a pattern (normally patchwork art) on the top layer. Comforters and Duvets typically have a single sheet of fabric for the top layer. Quilts can also have a single sheet top layer, in which case they're called a whole-cloth quilt, but they're not going to be readily distinguishable from a comforter or a patchwork quilt (if they use a patchwork print pattern) and as such shouldn't be taken into consideration.