when you eat and drink acid is produced that eats away at enamel.. and when you brush your teeth it also brushes away some enamel.

The reason your teeth still have enamel is that they are constantly being remineralized with minerals (including calcium) in your saliva being deposited on the top surface of the tooth.

If you consume less calcium, less calcium will be in your saliva, and that’ll slow that process down, while erosion continues normally (leading to sensitivity and eventually cavities)

if the problems he’s referring to are sensitivity (not related to gum disease), and he wasn’t getting enough calcium without milk, it’s quite possible that milk (calcium) reduced the sensitivity.

Nothing funny about it. One makes it clear it's a personal anecdote, the other states that "scientific studies show" - should be easy to show these studies then