Following quote is the abstract of a 1981 article, "The nature of freeze-induced white spots on orange segment walls," Raymond D. Bennett and Roger F. Albach, Journal of Agricultural and Food Chemistry 1981 29 (3), 511-514
DOI: 10.1021/jf00105a019 (full article is behind a paywall)
Exposure of oranges to freezing conditions causes formation of white spots on the walls of the fruit segments. The spots are actually located in the tissue comprising the separation zone between segments; when two adjacent segments are pulled apart, each white spot is split in half. The chemical nature of the white spot material was previously in dispute, but it has now been shown to be microcrystalline hesperidin coating the walls of cells in the separation zone. Freezing causes damage to cell membranes, and a soluble form of hesperidin located in the cell vacuoles is thereby released and crystallizes.
Hesperidin is a flavanone glycoside (naturally occurring flavor chemical) found in citrus fruits, so according to that 1981 research, the spots are caused if the orange was frozen. It can appear on oranges or tangerines.