Passing local variable by reference to a C++ thread

I was reviewing the code of a junior colleague and encountered the following code.

void ActionGetId(boost::property_tree::ptree& callInfo);
void ActionPutId(boost::property_tree::ptree& callInfo);

void handler(int type, std::string data)
{
    boost::property_tree::ptree callInfo(data);
    if(type == 0)
    {
        _ioService.post(boost::bind(&ActionGetId, callInfo);
    }
    else
    {
        _ioService.post(boost::bind(&ActionPutId, callInfo);
    }
}

They are passing a local variable by reference and then exit the function. When those functions are finally called, the local variable may not exist. Yet, this program doesn't crash. How is this working?