If the optional argument of the \chapter command should not be used but 'any' another free text, there are some ways, e.g. redefining \@currentlabelname to use \nameref still.
I provide a way with the powerful zref package for a new command named \labelshort[optional text]{labelname} and \nameshortref and establishing a new label property shorttitle and having some more flexibility.
Use the optional argument of \nameshortref to add some more explanatory text or correct grammar.
\documentclass{book}
\usepackage{xparse}
\usepackage[user,hyperref]{zref}
\usepackage{hyperref}
\makeatletter
\providecommand{\@currentshorttitle}{}
\zref@newprop{shorttitle}{\@currentshorttitle}
\zref@addprop{main}{shorttitle}
\NewDocumentCommand{\labelshort}{om}{%
\begingroup
\IfValueT{#1}{%
\renewcommand{\@currentshorttitle}{#1}%
\zlabel{#2}%
}%
\endgroup
\label{#2}%
}
\NewDocumentCommand{\nameshortref}{O{}m}{%
\zref@ifrefundefined{#2}{%
}{%
\hyperlink{\zref@extract{#2}{anchor}}{#1\zref@extract{#2}{shorttitle}}%
}%
}
\begin{document}
\chapter{Introduction: this is the first theory}
\labelshort[Introduction]{intro}
\section{Foo section}\labelshort[Foo]{foosect}
\clearpage
See \nameshortref[In the ]{intro} or \nameref{intro} or \nameshortref[in the ]{foosect}
\end{document}
