Titlesec / AutoFakeBold making pdf figures bold

I have a simple MWE similar to the following:

\documentclass[12pt]{article}
\usepackage[letterpaper, left=19mm, right=19mm, top=3.52cm, bottom=2.84cm, headheight=38.7pt]{geometry}
\usepackage{graphicx}

% set the font of the document
\usepackage{fontspec}
\setmainfont[AutoFakeBold=1.5, AutoFakeSlant=0.2]{Arial}

% table materials
\usepackage{booktabs}

% define colours
\usepackage{xcolor}
\definecolor{my-orange}{RGB}{238,113,43}

% title materials
\usepackage{titling}
\usepackage{titlesec}
\titlespacing\section{0pt}{6pt plus 4pt minus 2pt}{6pt plus 2pt minus 2pt}
\titlespacing\subsection{0pt}{6pt plus 4pt minus 2pt}{6pt plus 2pt minus 2pt}
\titlespacing\subsubsection{0pt}{6pt plus 4pt minus 2pt}{6pt plus 2pt minus 2pt}
\titleformat*{\section}{\Large\color{my-orange}} % \bfseries
\titleformat*{\subsection}{\large\bfseries}
\titleformat*{\subsubsection}{\normalsize\itshape}

\usepackage{microtype}
\usepackage{lipsum}

\begin{document}

\section{Section 1}

\begin{center}
\begin{tabular}{cccccc}
\toprule
A & B & C & D & E & F\\
\midrule
1 & 2 & 3 & 4 & 5 & 6\\
\bottomrule
\end{tabular}
\end{center}

\subsection{Subsection 1}

\lipsum[1]

\subsection{Subsection 2}

\begin{center}
\begin{tabular}{ll}
\toprule
Field 1 & Value \\
\midrule
Variable One & Testing \\
\bottomrule
\end{tabular}
\end{center}

\subsection{Subsection 3}

\begin{center}
\includegraphics[width=1\columnwidth]{graphs.pdf}
\end{center}

\end{document}


Which looks like the following when compiled with XeLaTeX:

The graph is a PDF created using matplotlib in Python. It isn't meant to have any bold text and is meant to look like this:

So why is the document compiling the figure with bold text?

I suspect it's something to do with the use of AutoFakeBold or the \titleformat commands section commands.