I mean, but presumably you do know he's described as having relatively darker skin than we'd consider "white"? And dark hair and initially dark eyes? Or is this one of these "Rue"-type situations where some part of the audience hears "tan skin" or "brown skin" and just thinks he's a white with a tan rather than that's his natural tone? Notably fan art gets it right as usual (the same is true of Wheel of Time - a lot of fan art showed the characters as darker than white-skinned, because in the books, notably Rand is paler than the rest, and the first city they come to, the author explicitly calls out everyone but Rand as being in the middle skin-tone range, neither pale or nor very dark).
I think what Sanderson is indicating here specifically is, based on Kal's description, he'd probably be played by a South Asian actor (Bollywood and similar have a near-infinite supply of handsome South Asian dudes, and Britain doesn't exactly have a shortage either), rather than East Asian, which may be what you're thinking (though I could be mistaken). Though another potential objection re: Cavill would be that canonically Kal is like 6'6" and Cavill is 6'1" on a good day (which means he's shorter than me lol and I don't think I'm hugely tall). Presumably that latter would be sorted out by just casting everyone like 6" shorter than they are in the books because it'd be pretty hard to find people as tall as they are in that.
I think most of the characters in Stormlight have skin tones which means few, if any, "white" actors could play them, apart from Shallan and Szeth (and Szeth, I get the vibe that he'd be played by an East Asian actor for some reason, but maybe that's just me).