The Ubuntu installer is called ubiquity. The changelog of ubiquity 2.3.18 mentions

"Use dmidecode to get a more unique suffix for the hostname (LP: #628087)."

The exact python code is:

def dmimodel():

    model = ''

    kwargs = {}

    if os.geteuid() != 0:

        # Silence annoying warnings during the test suite.

        kwargs['stderr'] = open('/dev/null', 'w')

    try:

        proc = subprocess.Popen(

            ['dmidecode', '--quiet', '--string', 'system-manufacturer'],

            stdout=subprocess.PIPE, universal_newlines=True, **kwargs)

        manufacturer = proc.communicate()[0]

        if not manufacturer:

            return

        manufacturer = manufacturer.lower()

        if 'to be filled' in manufacturer:

            # Don't bother with products in development.

            return

        if 'bochs' in manufacturer or 'vmware' in manufacturer:

            model = 'virtual machine'

            # VirtualBox sets an appropriate system-product-name.

        else:

            if 'lenovo' in manufacturer or 'ibm' in manufacturer:

                key = 'system-version'

            else:

                key = 'system-product-name'

            proc = subprocess.Popen(

                ['dmidecode', '--quiet', '--string', key],

                stdout=subprocess.PIPE,

                universal_newlines=True)

            model = proc.communicate()[0]

        if 'apple' in manufacturer:

            # MacBook4,1 - strip the 4,1

            model = re.sub('[^a-zA-Zs]', '', model)

        # Replace each gap of non-alphanumeric characters with a dash.

        # Ensure the resulting string does not begin or end with a dash.

        model = re.sub('[^a-zA-Z0-9]+', '-', model).rstrip('-').lstrip('-')

        if model.lower() == 'not-available':

            return

        if model.lower() == "To be filled by O.E.M.".lower():

            return

    except Exception:

        syslog.syslog(syslog.LOG_ERR, 'Unable to determine the model from DMI')

    finally:

        if 'stderr' in kwargs:

            kwargs['stderr'].close()

    return model

LP: #628087

Edit:
You can browse yourself the code by downloading it with:

cd /tmp

apt-get source ubiquity