The expectation we set for our students is that for each hour of teaching time there should be an hour of additional study after homework. So if I see my class for 4 hours per week they should be completing homework and then 4 hours of additional study.
Within our subject (not RS) we expect at least one piece of additional reading, e.g. journal article, news article, reading from a secondary textbook from the reading list, per week. The rest of this time will come from rewriting and adding to notes, doing past paper questions etc. Revision should be an ongoing process, not shoved into a couple of weeks at the end of the course.
Is it possible that the teacher is trying to make them understand the jump from GCSE, and possibly scare them into doing more reading?
In terms of the teacher not explaining theories, it might be that it's simply not the right time to go through them, i.e. they'll be covered later, or link to a different part of the spec. But this should really be made clear to students - it'd be expected that they'd be given an outline of the specification, a reading list and a glossary to complete as they went along (or they'd create their own as they went along), to help them to understand where the different concepts and theories come together.
Or the teacher might be unclear themselves - it's a new spec and the content will be more complex and weighty than in previous years. Exam boards have had very little time to prepare for the new specs and so teachers have struggled to access sound and consistent advice about the ins and outs of certain aspects. I know from speaking to a colleague that one of the problems the OCR RS A-level course has faced is a lack of resources i.e. textbooks, because the course was accredited very late by Ofqual. She was determined to follow OCR but when it still hadn't been accredited in late June she was forced to switch to an exam board that was further along in the process.
Hope this helps.