I think a key indicator is "Does it hurt when I do this?"
If you heel strike while running barefoot, it hurts.
Heel striking while walking barefoot, however, in most cases or terrain types doesn't hurt, and is much more comfortable than trying to forefoot strike.
Especially if you're wearing shoes, it takes some effort to land forefoot first while walking, since our center of gravity is generally well back from where our feet hit the ground.
Another idea is to watch babies/young children walking. Instinctively or mechanically, when they take their first steps they tend to land forefoot first (or mid foot) as they are quite tentative and keep their center of balance over where their foot hits the ground. But as they grow accustomed to walking and learn to take longer strides they transition to more of a heel strike.
I don't think there is much research on foot strike while walking, since there is significantly less force involved.