Its probably just an orphan key (remnant) left behind after a prior cleaning. When MBAM looks for malware related registry keys it also looks for any physical files associated with them.
After a security vendor updates its product version or releases an update to definition databases, it is not uncommon for subsequent scans
to find detection of items, traces of malware files or remnants of registry entries which had previously gone undetected (not reported) by prior scans long after the initial infection was removed. In that same manner, it is not unusual for a detected threat to no longer be detected during subsequent scans after a database update. This can be attributed to further testing after users have submitted a sample file which is then determined to be false positive
and removed from the detection list.