Diphenhydramine is the name of the drug. It's in many over the counter medicines. Unisom, Benadryl, Sominex, Banophen, Diphenhist, Aller G Time, Hydramine, Night time sleep aid, Pediacare Children's Allergy, Alka Seltzer Plus Allergy, Vicks ZZZ Quil Night time sleep, Nytol, etc.. there's many products that contain it. It's not important the product it was in, so the tests look for diphenhydramine, not each product that contains it.
It can be used for allergies, for sleep, for motion sickness. We don't know what it was used for, maybe a legitimate need, nor the dosage. They could have been given massive amounts for sedation, but it could have been for allergies at a regular dose.