I was being serious. Absent any injuries, musculoskeletal conditions or autoimmune disorders, the possible causes for swelling might include reactions to insect stings/bites, animal bites, contact with irritant plants, topical agents including skin lotions, sunscreen, or the sun itself. Some folks do experience "hives" from sun exposure, even without a sunburn.
Yup, I've experienced those on rare occasions, affecting my arms and/or hands. It was rarely the same thing twice. Swelling from sun, even without a sunburn -- often exacerbated by other medications, including aspirin or NSAIDs. On another occasion it was a reaction to a common antibiotic. On other occasions it was due to animal bites -- once a squirrel I tried to feed, two or three other times from cat bites and scratches, resulting in cellulitis.
And reactions to poison ivy, oak or sumac. Reactions to stinging nettles and other plants with fine spines or barbs. It's possible to rub against those without realizing it during a ride or walk around dense foliage. In some susceptible people it can occur from roadside mowing stirring up the allergens that stick to the sweaty skin and provoke a reaction.