If you ask someone how they're doing, they'll usually provide a short answer like “well, thanks,” even if they're having a bad day. No one wants to go into detail about their present state because of the length of time it would require to explain all the details. The truth may sound something like “I was late to work because the kid got sick, and then someone nicked my car.”
If you ask someone about their day when they come home from work or school, you can expect the same desultory answer most of the time such as “It was ok. Same old. The usual. You know…” Even the asking can be just as routine as the answer. You could probably get a better glimpse of your kid's day by looking at their Snapchat or Instagram.
For some parents, however, asking the common question can be a substitute for as Lisa Damour at the New York Times puts it, “I love you and miss you and would like to touch base.” Damour suggests asking your teen something more particular like status on a group project or basketball practice.
If you're going to ask either how someone is doing or how their day was and it's meant to be more than small talk, the interrogator's genuine interest, the tone of voice, and specificity is just as likely to produce an honest answer. Both ways can mean it. The truth is never banal.