I haven't read Fahrenheit 451 in a very long time, but I do remember this part. I think a possible reason as to why the author does this is to start creating conflict and introduce the real turning point of the story, when we find out what the real problem is. Hope this helped.
The answer would be b grain of the fabric is like grain of the wood. if you look at a plank of wood you see the lines going up and down it same thing really
