I mean the fact that he was repulsed by reading a book about dragons, but he's perfectly happy to read a book about SPACE dragons. You know, making fun of the elitist sci-fi types for looking down on fantasy for no real reason?
The difference, again, is in the definitional means.
Pern "dragons" = genetically engineered enlarged versions of existing naturally evolved small flying reptiles. The fire breathing is explained as the end result of an enzymatic reaction to certain minerals which they ingest when they need to produce flame.
All in alignment with science and scientific principles.
"Between" is a borderline case, BUT it operates by clear rules with regular, predictable results.
Fantasy "dragons" = creatures of and embued with abilities by supernatural, magical means. Fantasy fire breathing is totally without scientific explanation, simply being a property of "dragon-ness" for want of a better term.