Sorry, I just noticed that your match criteria is only under the file logging. You need to have your match also under the syslog host you want to send the messages to.
host x.x.x.x {
any any;
authorization info;
match "!.*Time since last watchdog strob.*";
port 514;
structured-data;
}
host x.x.x.x {
any any;
authorization info;
match "!.*Time since last watchdog strob.*";
port 514;
}