My husband was pulling weeds when he broke out in small red spots/fluid filled blisters and only on his upper torso. What could this be and treatment?

Poison ivy or…? There are many plants & weeds that can cause skin reactions, poison ivy being the most well-known. As long as there is no swelling of lips/throat or difficulty breathing, gently wash areas with mild soap & water to remove allergen. Use topical benadryl/aloe vera gel/ calamine lotion/ Cortaid (hydrocortisone) for rash & itching. Oral antihistamine like benadryl/zyrtec/claritin will help too. Not better—> see doc.
Unsure. Possibly dermatitis from the plants he was touching, or from any chemicals on the weeds. These lesions would likely need to be examined and more history obtained to be able to provide you with useful input about the diagnosis or possible treatment.