no, they use length to describe the measurement of the crack's width. totally valid afaic.
The correct word for a measurement of wideness is width.
Length [NOUN]: 1. the longest extent of anything as measured from end to end: the length of a river. 2. the measure of the greatest dimension of a plane or solid figure.
It's pretty unambiguously wrong. You can back into what the author meant without ambiguity, but that doesn't mean the author used the correct word.