Good heavens NO! It will NOT "void" his warranty. The car makers would love you to believe that there's such a thing as "voiding" your wty, but really, there isn't, at least not in the US. Voiding your bladder, yes; your wty, no. Under the Moss-Magnuson Warranty Act, the car maker must prove that something that you (or a 3rd party) did caused the failure for which you are making a wty claim. They must prove a link, establishin that act or omission on your part led to failure. Demanding oil change receipts you can't find WILL NOT SUFFICE! Anyone who gets told this needs to get a lawyer - right now.
So what if he goes 10k -- how can they link that to a failure - possible but remote. Now let's suppose you do something really stupid -- like run straight 60 wt racing oil in your new Ford in Anchorage in February. That would probably cause a provable failure and would generate a valid wty claim denial.
Now suppose you have the same broken Ford in Anchorage in February -- and the radio fails too. It's still covered by the wty, since Ford could never prove that the 60 wt molasses caused the radio to fail.
Claims can be denied, but it's often harder for the mfr to make it stick than you'd think, and the wty is virtually never truly "void".