One way to mask illicit adulteration is to add vegetable oil to boost the fat count and melamine to rig the protein figure.
It is suspected that the contamination occurred by direct adulteration with dried manure.
One thing to remember in all of this is that there have been examples of adulteration, deliberate and otherwise in homeopathy.
Word Origin and History for adulteration
c.1500, from Latin adulterationem (nominative adulteratio), noun of action from past participle stem of adulterare "corrupt, falsify; debauch; commit adultery," from ad- "to" (see ad-) + Late Latin alterare "to alter" (see alter).