I had a naturilized hoo-man citizen to my fort (applied for residency then applied for citizenship) get a full burial. She was a human dancer that I couldn't assign to my secondary tavern, but she liked steel. So I gave her some weaponsmith training to see if she could mood, but then a forgotten beast came into my fort through a hole a bloody tree left after felling it (another reason to hate nature!) and I lost her. My dorfs immediatley gave her a full burial in my catacombs.
The spoony hooman bard that drank himself to death in my booze stockpile was promptly ignored by my denizens until I marked his body for dumping. He was just a long-term resident iirc, but may have just been a visitor. I mostly remember the hooman dancer being a citizen over my dismay that I couldn't even make her a scholar, yet alone get her to perform somewhere else in my fort. I gave her a nickname after she became a citizen, too. You can freely memorialize those visitors and long-term guests, though.
TL:DR, its probably linked to citizenship status for non-dorfs. I don't know if that hooman would have returned as a ghost, but my dorfs immediately buried her without question.
Back to the OP's original problem... I really wish we could "de-invite" both guests and long-term residents alike. Some way to revoke their residency, or just kick them out. The first time I had a problem with this, was when I realized a long term resident (another hooman dancer) turned out to be a vampire. Since she was just a resident, I couldn't assign her to a burrow. I couldn't assign her as a militia captain either (squad of 1), nor order my military to gank her vampy ass. I eventually saw her wander into an empty temple and locked the door behind her. Years later she was miffed at being bored, but still perfectly fine. I eventually got around to diverting a forgotten beast into her room. Apparently web-spitting FB > vampire. I named him Bob. This was in 42.04 too, when Toady claimed to have reduced the number of vampires through implementing world-gen vampire purges. In all my years of playing DF, I had never encountered one before. I had 3 people die from 2 separate vampires (one was a migrant gem cutter) within 4 years of this fort created in 42.04 though.