As Torbjørn pointed, there is limited support for add items (modules in manual jargon) through the additions
library and the \smartdiagramadd
command. The main problem is that you can set only some global options for the added items.
This mean that individually you can control only the relative positions with respect main items (not with respect arrows) and in some extent the style of connection (basically, right, left or bidirectional arrows with/without head/tails, or none), but unlike show your image, you cannot set (as far I know) additional items with more than one type of font color, for instance. A minimal example of what you can / cannot obtain:

\documentclass{article}
\usepackage{smartdiagram}
\usesmartdiagramlibrary{additions}
\usetikzlibrary{shapes.geometric}
\begin{document}
\smartdiagramset{border color=none,
uniform color list=teal!70!black for 3 items,
module shape= ellipse,
module minimum height=2.5cm,
circular distance=4cm,
font=\Huge\sffamily\bfseries,
text width=5em,
text color=white,
arrow line width=8pt,
additions={
additional item font=\sffamily\bfseries\color{red!50},
additional item offset=3em,
additional item height=0em,
additional item text width=5em,
additional arrow color=teal!40,
additional arrow line width=4pt,
}}
\smartdiagramadd[circular diagram:clockwise]{B,C,A}{
right of module1/Text 1 without arrow,
above of module1/Text 2,
left of module3/Text 3,
above left of module3/Text 4,
below left of module2/{Something}}
\smartdiagramconnect{-}{module1/additional-module2}
\smartdiagramconnect{<-}{module3/additional-module3}
\smartdiagramconnect{<->}{module3/additional-module4}
\smartdiagramconnect{->}{module2/additional-module5}
\end{document}
additions
library, see section 3 of the manual.smartdiagram
manual does not provide any example that has additional test available, as you need it. You would probably be better off creating the whole thing intikz
directly. There is nothing insmartdiagram
that is not done withtikz
as far as I can see...