Most likely, someone that has your address on their computer got infected. The virus on their computer collected all the names in address books, web page cache, etc. It uses those names to spoof the sending address by altering the headers...when it hits an unreachable address, the host delivers a failure to whom it thought sent it....You.
Weber Smokey Mountain Cooker ?
Weber 22.5 One Touch Gold ?
Weber Smokey Joe Gold ?
Weber Grill Decency Agent # KTL9352