You should not be able to step flat footed on the ground while on the saddle if thats what this online person is stating.

You need to set the saddle height so you have proper extension when pedaling. The bike saddle is not for sitting when the bike is stopped. When you stop you get off the saddle.

No offense to your motorcycle safety course friend but they don't sound like they know much about bicycling.

A picture of your bike and you on it would help.