I wouldn't think you'd have to pay that back, imo. Wikipedia says it best: "A stipend is a form of payment or salary, such as for an internship or apprenticeship. Stipends are usually lower than what would be expected as a permanent salary for similar work. This is because the stipend is complemented by other benefits such as accreditation, instruction, work experience, food and/ or accommodation. Universities usually refer to money paid to graduate research assistants as a stipend, rather than as wages, to reflect complementary benefits".