[AKQJ10]

Well, if you want to get beyond the basics, there's a somewhat arcane way in which your friend is correct. IF YOU HAVE SOME INDICATION WHAT CARDS ARE IN YOUR OPPONENTS' HANDS, then you can use that to change your estimate of probabilities of cards coming out of the stub.

For example, in Omaha 8/b, many more good hands have low cards (e.g. A2xx, preferably A23x or A24x) than high cards (usually all four above a ten). If you're playing O8 with knowledgeable players, you're in late position, and many have limped in, your high hand might go up in value. This is because you reason they wouldn't be in the pot without low cards; therefore, the stub must be rich in high cards, and it's more likely that you'll hit, or at least that they won't and you can steal the pot with a bet.

That's a very advanced application of this concept, and likely well beyond what your friend means. If you know there are 9 spades among 47 unseen cards, you have no indication whether people contesting the pot with you have zero, one, or two spades. After the flop, if there are two spades on board, and several have called a flop bet, then you can make an inference that someone else might have two spades, so you might need to shade your probabilities down slightly. So maybe it's more applicable than I thought. But if you can't put them on more or fewer spades, then the applicability to flush draws is nil. And for that matter, if you limit your inference to hands with many flop callers, then we're only talking about two suited cards out of several, hence probably not changing the probabilities in any appreciable way!

So you definitely don't want to go shading your flush draw decisions very far based on this concept. Leave this for the O8 writers.