Misidentification of arithmetic expansions

Where the bash(1) reads

       ((expression))
              The expression is evaluated according  to  the  rules  described
              below  under ARITHMETIC EVALUATION.  If the value of the expres‐
              sion is non-zero, the return status is 0; otherwise  the  return
              status is 1.  This is exactly equivalent to let "expression".

explainshell gives this instead:

       (list) list  is  executed in a subshell environment (see COMMAND EXECU‐
              TION ENVIRONMENT below).  Variable assignments and builtin  com‐
              mands  that  affect  the  shell's  environment  do not remain in
              effect after the command completes.  The return  status  is  the
              exit status of list.

It's a great project btw. :)

Start with the explainshell example command and compare its classification with the bash(1) manual text quoted in the issue. Trace how (( foo )) is parsed and matched against the arithmetic-expansion documentation versus (list), then verify that the example is identified correctly.