I think there is no actual rule or firm line between medical grade or commercial grade cannabis.
Medical grade normally refers to cannabis that is consumed to treat a condition or alleviate symptoms and is generally grown/produced by a registered, known producer. I guess for control purposes.
Many say it has to be organic or certain potency, but I think it just personal opinions.
If you don't know the vendor/grower/producer personally there is a high chance cannabis can be contaminated with anything ranging from pesticides, chemical fertilisers, etc., etc.
To me it is a touchy subject, as it totally depends on personal consciousness.
So, unless, I grow it myself, it is not medical grade to me. A gamble each time I purchase.
More to be grateful and thankful to those vendors in LB who are true to cannabis itself and cannabis culture.