Explanation of CAVP format for NIST Test Vectors for SHA-2 and 3
All of your questions are answered in the Validation System documents that are linked to by the algorithm test pages.  In this case, look at http://csrc.nist.gov/groups/STM/cavp/documents/shs/SHAVS.pdf

For this case, the message length is expressed in bits not bytes. The fact that the message is also encoded as value of 00 should be ignored in the test vectors smaller than one byte; this just adds confusion to the reader.

Len = The length of a message in bits