With so few employees, you don't fall under Federal law. Given that they didn't keep the temp long, that actually supports their position that it was a reduction in force. So it would be up to you to show convincing evidence that, but for your taking medical leave, you would not have been the one who was laid off. You may or may not be able to make a convincing case under state law, assuming that you have enough employees to be covered under state discrimination laws. ("Under 10" means you definitely are excluded from Federal but does not clearly indicate that you are or are not excluded from state.)