echo "$array[@]"

echo "${array[@]}"

Some languages use the syntax $array[index] to access an index of an arrays, but a shell will interpret this as $array followed by the unrelated literal string (or glob) [index].

Curly braces are needed to tell the shell that the square brackets are part of the expansion.

If you want the square brackets to be treated literally or as a glob, use ${var}[idx] to prevent this warning.

This does not change how the script works, but clarifies your intent to ShellCheck as well as other programmers.