I had the same discussion a few days ago and someone posted https://www.businessinsider.com/wuhan-coronavirus-risk-of-re... [It has a link to a video, but the caption of the video is wrong. The recommendation to the cured patients is not to increasing their physical activity but to enhance their own health safeguards.]

I found two other articles about the same case https://globalnews.ca/news/6623287/coronavirus-multiple-infe... and https://www.reuters.com/article/us-china-health-japan/japane... . t's not 100% clear, but it looks like a continuation of the first infection after a few week of no symptoms. It makes more sense than no immunity (at least at the short time), and a second independent infection.