Hi, look at his tongue. Does it look spotted? Almost like it might have blisters or burns on it?
My granddaughter has Geographic Tongue. This is a non issue 99% of the time but when the taste buds go wonky she gags and pukes up food she normally loves. It tastes totally different to her.
Some times it is very minuscule and only visible to me since I know what to look for. A pediatric dentist might be able to say if this is a possibility.
Otherwise from what you are saying, he is only eating foods that require little chewing. Soft foods....
He may be teething his 2 yr. molars or even the next ones, he may have a tooth that has a cavity, etc....the teeth do effect how we eat and sudden changes like this are usually due to a specific reason.
That's why I am thinking outside issue other that just deciding he only wants to eat dairy.
Thinking teeth issue, tongue issue, throat may be sore, stomach might have something and the dairy soothes it, may have some deficiency and body is craving calcium.
I tend to think outside the box. Just some thoughts that might lead you to ponder on a different aspect.
Here's some pictures of Geographic Tongue. Notice the 2nd one is very minimal. Then some are very disturbing. One might even think the person has drank boiling water.
http://www.picsearch.com/pictures/Health/Cutaneous%20cond...
http://www.primehealthchannel.com/geographic-tongue-pictu...