Nah, that was his 275 that came in the game where he shared that massive stand with Boucher. The game was the Third Test in 1999/2000 at Kingsmead.
His 210 was in the Third Test in 1998 at Old Trafford. SA piled-up a massive first-innings total but England pulled-off one of the greatest rearguards in Test history to save the game after losing 12 wickets while still 358 behind with over 5 sessions left in the match.
Both innings' were damn good, but I'd tend to rate the 275 as the better of the two. However, an even superior performance for mine was his match double of 130 and 60 at Headingley (yet again against England) in 2003. Curiously, he was dismissed by no-balls very early on in both the 130 and the 275. The 275 one, however, I've long believed he was distracted by the no-ball call and missed the ball (he'd have been lbw) because of that - he palpably changed his shot after hearing the call, IMO. Ridiculous that Philip Tufnell was bowling no-balls off 5 paces anyway.
Flintoff's got a bit more excuse, but still - if his foot had been behind the line, maybe just maybe the ball would've been different.