Is a burning candle a source of heat?
Yes. If you put your hand in or near a burning candle, it is hot, meaning a burning candle is a source of heat.
An exothermic reaction involves the release of heat into a system. The burning of a candle is combustion reaction. Combustion reaction release heat, and this can be detected and measured by the burning of a candle's wax. From these testable observations it is determined fact that candle burning is indeed exothermic.