
I went away a month ago and left my 2 year old with a dog sitter. I gave her specific instruction re: feeding, sleeping, walking etc. My girl is raw fed.
I came back to find that the sitter had been giving her 'titbits' off her plate whilst she was eating(she felt guilty eating whilst my girl was watching her) and consequently, my very clever girl started to refuse her food. After two days of not eating, the sitter, without even phoning me, went to the supermarket and bought her some small tins of Bakers!!!!!ugg. She happily ate these.
My girl sleeps in the study next to my bedroom but because she whined the first night (she is a good actress) the sitter then allowed her to not only sleep in my bedroom, but also on the bed.
She asked, before I left, if she could take her out in the car at times. I said yes, but she must go in a crate ( prepared one for her). The sitter ignored my wishes and just took her in the footwell after me saying that she is not to travel in the front of the car in the footwell.
I also said, that she has to be kept on her lead at all times and to keep her walking to heel ( it has taken me an age to stop her pulling) She also ignored this and decided to walk her on a 'flexi', which I absolutely abhore (she brought one with her). Told me what a good time she had running here, there and everywhere and having a good sniff.
I have had the devil's own job to correct all the above, so I would go with the advice of the previous posters and feed him what your friend wishes him to be fed even if it is not your choice. As you stated, he is taking treats ok. When he is hungry, he will eat.