Creating a background image on the title page only using Beamer

Enclosing \usebackgroundtemplate by { ... } applies the command within the scope. Place your title page frame within the scope like so:

\documentclass{beamer}
\usetheme{Antibes}
\usepackage{graphicx}
\usepackage{tikz}

\title[...]{My title}
\begin{document}
{
  \usebackgroundtemplate{\includegraphics[width=\paperwidth]{back.pdf}}
  \begin{frame}
    \titlepage
  \end{frame}
}

\begin{frame}{History}
    This is a test page!
\end{frame}

\end{document}

With \setbeamertemplate{title page}{...} you can modify the title page without effecting global setting.

\documentclass{beamer}
\usetheme{Antibes}
\usepackage{graphicx}
\usepackage{tikz}

\pgfdeclareimage[width=\paperwidth]{mybackground}{back.pdf}

\setbeamertemplate{title page}{

        \begin{picture}(0,0)

            \put(-30,-163){%
                \pgfuseimage{mybackground}
            }

            \put(0,-110.7){%
                \begin{minipage}[b][45mm][t]{226mm}
                    \usebeamerfont{title}{\inserttitle\par}
                \end{minipage}
            }

            \end{picture}

    }

\title[...]{My title}

\begin{document}

    \begin{frame}[plain]
        \titlepage
    \end{frame}

    \section{Introduction}

    \begin{frame}{History}
        This is a test page!
    \end{frame}

\end{document}