To elaborate on this (quoting my own post but idc), an infected person can start spreading the virus 2-3 days before they experience symptoms or test positive. So the general opinion around the NFL of "test negative and you're good" is a little reckless, because some of those negatives are spreading the virus. These recent positive tests for the Titans were testing negative too the day prior, and may have been spreading the virus to the rest of the team if facilities weren't closed.
And having Cam Newton around your team on Friday, then traveling and playing a game on Monday and just assuming that everyone else is fine because they haven't yet tested positive is...questionable at best