Drop B tuning is a heavy metal guitar tuning for a six-string guitar where the strings are tuned to B-F#-B-E-G#-C# (or B-G♭-B-E-A♭-D♭). This is a "drop 1" tuning in the key of C# (i.e. tune the whole guitar down a minor third from standard tuning, then the 6th string is lowered an additional whole step down). As a result, it uses the same fingering as all other "drop" tunings.
Heavy metal guitarists rarely use Drop B tuning when tuning their guitars.  
My statement is definitely incorrect because the context states that Drop B tuning is a heavy metal tuning for guitars.  If so, it is incorrect that heavy metal musicians would "rarely" use it.  In fact, they probably use it frequently.  The system might have found it difficult because the system did not know the meaning of the word "rarely" or because it did not know what a heavy metal musician was.  