I guess COVID-19 creates unique cough sounds, Resapp is not the only team researching this, see these examples:
https://spectrum.ieee.org/ai-recognizes-covid-19-in-the-sound-of-a-cough
https://www.arc.gov.au/news-publications/media/research-highlights/smart-diagnostics-ai-tech-can-hear-covid-cough
https://pubmed.ncbi.nlm.nih.gov/32839734/