Why does Google Chrome report that this web site is not secure?
Because it is not. Walkbikepaloalto.org is hosted on a basic web server account, without security certificates which would allow a Secure HTTP connection (https://) instead of basic HTTP (http://) . This means there is no secure way to transfer user, password, or financial information to this site.
Should you be concerned? No, because this is only an informational site, and there are no internet connections for walkbikepaloalto.org which would require a secure HTTPS connection.