That number is so low it makes me wonder if it was a QC issue in the lot.
Out of curiosity, I did the same test using municipal water
and the 3 base malts I have on hand. The outcome:
Rahr 2-row: 6.10
Crisp MO: 5.89
Castle Pils: 5.69
More than anything, these tests were to prove a point to my local friends who do nothing to their water apart from using a charcoal filter or campden tablets...and they tease me for claiming water is one of the most important ingredients in beer.