Wise interview questions

Had a couple of HR interviews first. Then they gave me a home assignment, fairly complex. I finished and sent it to them, after around a week I got a mixed up feedback. It was pretty biased towards certain things they like and seems like if you do things some other way it's considered as a bad practice. Anyway, after that I got a technical one hour online interview with them, where they asked me to find issues with their code and suggest some things. Also asked me a whole bunch of different questions iOS and programming related, like stack/heap, memory management etc. After that I got a rejection letter with a pretty weird feedback. They gave me good and bad impressions, in which they contradict themselves. Like in "good" section they say I was very well prepared for the technical interview and knew my stuff, and then in "bad" section they say I wasn't prepared because I forgot some exact syntax of some function. Who the hell cares if one remembers the exact syntax if he knows his stuff anyway? Also, they said some really weird things like "You don't challenge your clients enough..." - what does it even mean?! How a developer working on some company making a product for it has to "challenge" its clients? Make it harder for them to use the app or something? Anyway, quite disappointed with such a biased and subjective feedback. Oh, and I needed to chase them after every step of the hiring process because they're apparently too busy to reply.