It sounds like they received an oil and gas lease offer on their mineral interest or an offer to participate whereby rather than just receiving a 1/4 or less royalty plus other terms of lease offer, as a participant if production is obtained one receives 100 percent of their interest but also bear expenses in the drilling and maintenance of well. If it is a dry hole, they receive nothing. This is a standard industry practice made by the company/operator on an unleased minerals prior to drilling the well. You either opt to lease, participate or may be force-pooled in some states. It certainly does not sound suspicious.