The so-called lava tube is created when when lava follows a natural channel during an eruption. During the course of the flow as the outer portion of the channel cools, it creates a tube through which the still molten lava flows; at some point the flow is blocked by cooling rock at it source but the lava itself continues to flow, leaving the tube in its wake.
It looks like this before:
Once cooled they look more like this:
Interesting theories,but far more like these strange caves are not caused by lava at all, but rather wholly differnt!