To Clarify the Difference between buttermilk vs yogurt:
YOGURT: Yogurt is produced by a mixed culture of two types of bacteria. Imbedded in particles of the protein casein, you will see chains of ----cocci or diplococci(Streptococcus thermophilus) and big rod-shaped bacilli (either Lactobacillus acidophilus or L. bulgaricus)----. If you do a Gram stain, the bacteria will be Gram positive (purple) and the protein will be pink. The illustrations at the top of the page are micrographs I took of a Gram stain of yogurt. The purple rods are Lactobacillus, the purple spheres are Streptococcus. The pink globs are casein, milk protein.
BUTTERMILK is the fermentation of milk by a culture lactic acid-producing ----Streptococcus lactis plus Leuconostoc citrovorum---- which converts lactic acid to aldehydes and ketones which gives it its flavor and aroma.
If one will take the time to study the Different kinds of Bacteria used to make Yogurt vs Buttermilk it should be obvious there is a Great Difference!