This is not the log, this is the dump of problem data. You have requested a binary format which is not human readable, and then additionally gzipp-ed.
Try
"dump.ptf"
or any other format from
that you like ("dump.mps", "dump.cbf", etc.) The file format will be determined by the extension.
If you actually want the optimization log output then you just get it to the Matlab window if you set Yalmip to be sufficiently verbose.
Michal