I assume the issue with him flying out a few days later is that he would have had to get a scheduled flight(s) and mix with a load of other random passengers. He would then have to quarantine after arriving in SA or risk infecting the rest of the squad if he caught something en route. The BA flight from Edinburgh to Jo-burg was essentially a chartered flight/secure bubble for the Lions players, coaches and staff.
I was also surprised he made it TBH but I'm probably more surprised he made it into today's match day 23. Surely better to save him for Weds or next Sat if he passed RTP protocols.