Q:

Arrow not required (TikZ)

I do not understand the presence of the red arrow in the table
\documentclass{standalone}
\usepackage{tikz}
\begin{document} 
\begin{tikzpicture}
\foreach \x/\xtext/\ytext in{0/x/y,1/1/4,2/1.5/6,3/2/8,4/5/20}
{\draw (\x,0.5) +(-0.5,-0.25) rectangle ++(0.5,0.25) ;
\draw (\x,0) +(-0.5,-0.25) rectangle ++(0.5,0.25);
\node[]  at (\x,0.5) {$\xtext$};
\node[]  at (\x,0)   {$\ytext$};
}
\draw[color=red,->,thick,>=stealth,shorten >=2pt,shorten <=2pt] (4.5,.65) edge [distance=1.2cm,bend left=80 ] node [right]{$\times 4$} (4.5,-.15);
\end{tikzpicture}
\end{document} 

A:

I don't know why it is there either, but it disappears if you write
    (4.5,.65) to [distance=1.2cm,bend left=80 ] node [right]{$\times 4$} (4.5,-.15); instead of
    (4.5,.65) edge [distance=1.2cm,bend left=80 ] node [right]{$\times 4$} (4.5,-.15); (Notice to instead of edge)
\documentclass{standalone}
\usepackage{tikz}
\begin{document} 
\begin{tikzpicture}
   \foreach \x/\xtext/\ytext in{0/x/y,1/1/4,2/1.5/6,3/2/8,4/5/20}
      { 
        \draw (\x,0.5) +(-0.5,-0.25) rectangle ++(0.5,0.25) ;
        \draw (\x,0) +(-0.5,-0.25) rectangle ++(0.5,0.25);
        \node[]  at (\x,0.5) {$\xtext$};
        \node[]  at (\x,0)   {$\ytext$};
      }
      \draw[color=red,->,thick,>=stealth,shorten >=2pt,shorten <=2pt] (4.5,.65) to[distance=1.2cm,bend left=80 ] node [right]{$\times 4$} (4.5,-.15);
\end{tikzpicture}
\end{document} 

A:

An edge is a separate path which inherits, by default, all the attributes of its parent. Hence, an arrow tip is added to the main path and to the edge. However, you want it only for the edge. Hence, just don't add it to the main path.
\documentclass[border=10pt]{standalone}
\usepackage{tikz}
\usetikzlibrary{arrows.meta}
\begin{document} 
\begin{tikzpicture}
  \foreach \x/\xtext/\ytext in{0/x/y,1/1/4,2/1.5/6,3/2/8,4/5/20}
  {\draw (\x,0.5) +(-0.5,-0.25) rectangle ++(0.5,0.25) ;
    \draw (\x,0) +(-0.5,-0.25) rectangle ++(0.5,0.25);
    \node[]  at (\x,0.5) {$\xtext$};
    \node[]  at (\x,0)   {$\ytext$};
  }
  \draw[color=red,thick,>=Stealth,shorten >=2pt,shorten <=2pt] (4.5,.65) edge [distance=1.2cm,bend left=80, -> ] node [right]{$\times 4$} (4.5,-.15);
\end{tikzpicture}
\end{document} 

Alternatively, you can avoid using an edge. Then you have just one path and TikZ will use just one arrow tip, as noted in balcinus's answer.

