Well the main point with a lot of language is that it isn't used very carefully. "Fossilised" may not be quite adequate, but what *is* certainly possible is that a sort of air-thight seal was created around the object containing the DNA. (This tends to happen with stuff caught in a mud-flood for instance.) Such a seal would have prevented much of the "usual" damage DNA would undergo, though it must be said that DNA is a highly unstable substance so the object containing the DNA must have been very large or by default very isolated (e.g.: parts of the root of a tooth).