I'm 5'8" and my forearm is 10.5". The correlation between height and the length of your forearm is smaller than you think.
Not in the context of this discussion - i.e the fact that big-cock pornstars being as long as their (usually tiny) female co-stars' forearms does not support the contention that they are upwards of 9 and 10" long (bearing in mind that these comparisons are misleading anyway, given that they are always from the side or below).
In any case you seem to have missed the finer points of the statistics I quoted. As I pointed out 10" is greater than 95th percentile for arm length in women - maybe 97th or so. In other words probably only three or four in a hundred women have a forearm this length.
5'8" is tall for a woman in the US - average height is 5'5" or thereabouts. The correlation between height and forearm length may not be precise, but there is a correlation. Few of the very small percentage of women who have a forearm length of 10" or more are going to be of even average height. The number of women with a forearm length in this region
below average height is likely to be negligible. Such dimensions would be noticeably incongruous on a petite woman, even on film. I'd bet a lot of money that none of the slight, 5'0", 5'1" and 5'2" female co-stars often found in big cock-porn have forearms anywhere near 10" in length.
Given that measurement from the side can add about an inch to properly measured NBP length (certainly in the BS way its done in porn) a pornstar of 6 or 7" NBP length could easily appear to be as long as the forearms of the small girls often used in big cock-porn when compared in this way. After all, they use girls of this stature precisely in order to exaggerate the size of the penises on show. 7" NBP is a very big penis in the real world, so these guys are not by any means average, but neither are they routinely 9, 10 & 11" or more, as the gullible would have us believe.