Pardon me, OBR, it's not related to birds and bogeys but only to gross score.
Therefore, an indication of "6 under" doesn't help. Was it 6 under over 18 holes at STA, giving a gross score of 66, or 6 under on the front nine of OLY, giving a sensational 28 (x2 = 56 for average calculation)?
Nevertheless, all Tour Legends are new in their trade, therefore it's safe to say that their average does float, until a number of ranked rounds above 500 (well above I'd suppose, maybe up to 1000 (just a wild guess)).
OTOH their average will be around or below 60, which corresponds to 6 under (30 => 60) at STA. A floating average will only drop when the score added is below the average itself, so this will be true.
As for Ike, a Legend around 60 average, you must have had a score higher than 65 in your 500 rounds counting in (yes, you are out of the floating zone), and the 65 replaced it for a better result. That said, all those nice 31s and 32s (= 62, 64) must have changed your average, too.
Now we know the difference in calculation:
You are out of the floating zone, your friend is within, resulting in different reactions on the same scores.