Ah, that's what you're getting at. Yeah, I retract the stronger claim. He could be good at chess. It would just not be likely.
Based on my experience, it's more likely than him being a wizard.
IDK, all children born to two wizard parents that I know are also wizards!
Which reminds me of a fundamental flaw in the racism allegory presented in the Harry Potter books. As far as we can tell, in the Harry Potter universe, wizarding ability is a recessive gene. If that is the case (and it is definitely the case that wizards have a much higher chance of spawning a wizard than muggles do), then the "pure-blood" ideology... kind of makes sense.
In hpmor, Harry hypthesizes that it could be based on exactly 2 genes (or chromosomes?). So each person has 2 wizard genes, they either say "magic" or "no magic". If both say no magic, you're a muggle. If it's split, you're a squib. And if it's magic/magic you're a witch or wizard. If two people have kids, each kid gets one gene from each parent randomly. So two wizards get 100% wizard. Wizard/Muggle always get squibs. And Squib/Squib have 25% muggle, 50% Squib, and 25% wizard. They find that this fits the data.
That's one way where the ideology wouldn't make sense, at least insofar that Hermione has no disadvantage compared to malfoy. If on the other hand it depended on 100 genes and more wizard genes make more wizardy wizards, then it would make sense. Two parents with n/wizard genes each where n > 50 would have kids with an expected number of genes m with m > n.
But in the universe, the data seems to be prett clear on it not making a difference. If anything mudbloods tend to be stronger.