I don't think a broken pipeline is the case -- unlike our pipelines, these ones are buried several feet underground. Pipelines don't just unearth themselves: someone deliberately dug out and punctured it, in an attempt to steal gas.
A small bit of information about what's growing on the field (alfalfa), the date it happened and what farm equipment are generally used at the time would make it pretty easy to conclude.
So just because you're not convinced doesn't mean they aren't right.