Simmons reportedly left New York City, where the team was spending an extra night following their game against the Brooklyn Nets on Thursday after learning of Seth Curry's positive test for COVID-19. But according to Rivers, this was just a matter of confusion.
Per Derek Bodner of The Athletic, Rivers said Tuesday that Simmons was "unaware" that players couldn't return to Philadelphia, and the 24-year-old turned around once he received the call to head back to New York.
Rivers said Simmons was one of a number of players who started to find their own way back home, but he was the only one who made it anywhere before learning that the team would stay put.
Simmons did not play Saturday, a last-minute decision that resulted in the team being handed a $25,000 fine for a violation of injury-reporting rules. With Simmons sidelined and the team conducting contact tracing following Curry's positive test for the virus, only seven players took the court against Denver that day.
He did not travel with the team to Atlanta, where they faced the Hawks on Monday, though he was not listed on the injury report ahead of the team's Tuesday game against the Miami Heat, who are similarly depleted due to the league's health and safety protocols.
Miami has eight players out and will suit up with the league minimum of eight, while the Sixers will have 10 players available, including Simmons and Joel Embiid, the latter of whom did not play Saturday because of back tightness.