The answer here is simple: the data is valid and formatted according to Annex B, prefixed by start codes 00 00 00 01
and not run length encoding.
H.264 extradata (partially) explained - for dummies
Annex B format
in this format, each NAL is preceeded by a four byte start code: 0x00 0x00 0x00 0x01 thus in order to know where a NAL start and where it stops, you would need to read each byte of the bitstream, looking for these start codes, which can be a pain if you need to convert between this format and the other format.
More details on H.264 spec - freely available for download. Page 326 starts with "Annex B - Byte stream format".