J.S.
My 10 month old just went through this a few weeks ago because she was teething. I was worried too because she had really just started liking and accepting so many foods and, not realizing she was teething, I was dismayed at her wanting to breastfeed non stop again. You may want to consider this since he only wants liquids and harder crackers. My daughter's appetite worked itself back to where it was the next week. I read it is very common for teething babies to prefer liquids and especially the comfort of nursing during that time.
Oe other thing is that my daughter seems to go through phases of textures she likes, as well as a preference for warm or cold food. She stopped eating meats until they were nice and warm for her.