The point of contention is not that the bible says god created the earth in 6 days, not 7, nor is it the fact that the Judeo-Christian creation story is being singled out, effectively ignoring the creation myths of other religions or cultures, but rather, this man is upset that the biblical creation story has been called a "myth".
It seems to me that a quick look-up in the dictionary could have saved him a lot of trouble...
Here's how Webster's defines myth:
1. a usually traditional story of ostensibly historical events that serves to unfold part of the world view of a people or explain a practice, belief, or natural phenomenon
2. a popular belief or tradition that has grown up around something or someone; especially : one embodying the ideals and institutions of a society or segment of society
To me, both of these definitions of the word myth suggest that it is the ideal word to describe the biblical account of creationism. Myth, in this sense, does not mean "made-up story" but rather a story that is central to a belief system, or one that is popular within a certain tradition or segment of society and offers up some explanation of the origin of their beliefs. I don't think one could come up with a more perfect word.
Of course, this man's ire is the result of the other definition of "myth" which Webster's lists as its 3rd definition: a person or thing having only an imaginary or unverifiable existence. However, even if this usage was intended, it still doesn't strike me as slanderous. The biblical creation story is unverifiable, there is no other text to refer to in order to corroborate the story, no physical evidence, nothing else to verify the tale, which is why it is an article of faith. And, as the evidence from the fossil record shows, all of the plants and animals and other living things on this earth were NOT created in 6 (or 7) days, but rather, they evolved over millions of years. Therefore, a story that claims everything was created in less than a week is clearly imagined, and is, at best, an allegory.
All that being said, however, I would propose a solution that should make everyone happy. Rather than singling out Judeo-Christian creationism, the book in question should be amended to define creationism as "any myth that suggests the earth, and/or all of the living creatures inhabiting the earth, were created by a supernatural being, or supernatural force, rather than by natural causes over long periods of time." In this way, no one belief system is targeted, and all forms of creationism (from intelligent design to Greek and Norse mythology) are cast out of the science classroom.