Been a Ham for over 30 years and have not heard of this ARRL award.
Perhaps it’s something the ARRL just cooked up! This award is available to amateurs who have contacted at least 100 DXCC entities while operating mobile. Contacts made any time in the past count and no QSLs are required. The Mobile DXCC is a one-time award and is non-endorsable. You do not have to be an ARRL member to qualify!