In the following code, the only difference between fun1() and fun2() is
that in the former the expression "false && true" is within an extra set of
braces but that's enough to make them behave differently. Calling the
fromer doesn't trigger an exit while calling the latter does.

#!/bin/zsh -e
>
> function fun1() {
>     { false && true }
> }
>
> function fun2() {
>     false && true
> }
>
> echo aaa: $?
> false && true
> echo bbb: $?
> fun1
> echo ccc: $?
> fun2
> echo ddd: $?
>

The output of the script (with Zsh 5.8 on Linux and Zsh 5.8.1 on macOS) is
the following:

aaa: 0
> bbb: 1
> ccc: 1
>

The documentation of ERR_EXIT mentions the special case of conditional
expressions. I understand that the command "false" by itself in the
expression "false && true" shouldn't trigger an exit since it appears in a
position where a condition is expected. However, since the expression
"false && true" as a whole evaluates to a non-zero status and doesn't
appear in a position where a condition is expected, I would assume that it
should trigger an exit. Thus, in my opinion the script should have the
following output:

aaa: 0
>

That's obviously not the case. Apparanty Zsh simply ignores non-zero
statuses of conditionals if they weren't generated by the last command.
However that doesn't explain why the call to fun1 doesn't trigger an exit.
Like the call to fun2, it returns with a non-zero status but for some
reason only the latter triggers an exit.

Note that the following functions behave like fun1 and don't trigger an
exit when they are called.

function fun3() {
>     if true; then
>         false && true
>     fi
> }
>
> function fun4() {
>     case foo in
>         * ) false && true;;
>     esac
> }
>

And the following function behaves like fun2 and triggers an exit.


>  function fun5() {

    ( false && true )
> }
>

Philippe