That's not quite true.
When lithium batteries fail in the manner being discussed here they experience what is called a "
thermal runaway". Certain conditions within the battery lead to an increase in heat which feeds on itself and so it gets hotter and hotter, eventually resulting in a lithium metal fire. (which is very hard to extinguish) The heat causes the battery's electrolyte to expand until it bursts, releasing large amounts of hot flammable gas in the form of a fine mist which ignites when it suddenly comes into contact with oxygen in the air and releases a lot of energy very quickly. It is only when this reaction takes place inside a confined, sealed space where the rapidly expanding burning gases cannot escape that you end up with an actual explosion. So for example, if a lithium-ion battery experiences a thermal runaway inside a tightly sealed metal flashlight it becomes in essence a pipe bomb and will explode. In other devices like dash cams, where the lithium battery is a foil pouch inside a plastic camera, the battery will generally swell up and might even catch fire if it bursts but it is unlikely to explode in the classic sense of what we can legitimately define as an explosion.
