First, it is a guide, or collection of advice. Sometimes it will say 'this is right', or 'this is wrong'; but more often it will say 'this is preferable', or 'in academic English, avoid this'. In other words, many articles concern stylistic choice. Readers have personal tastes, and your teachers may not agree with something you learn from this guide. That is fine: we don't necessarily agree with their choices either, and one of your teachers may disagree with another one. (They often do.) As a learner, you must develop your own style - and all good styles are individual. So pick and choose between your sources. Good writers consider their readers - and a student writing an assignment should consider the marker, and therefore the marker's prejudices.
Second, AWE is designed with the needs of students in Higher Education in mind. This level of writing about which it advises is formal, and careful in tone, although, like many teachers, it may itself sometimes be chattier. The advice here may be very useful to other writers - we hope it will be - but the details may not always be helpful to them in the same way as to students seeking to develop an academic style. Students who are approaching Higher Education - those in Sixth Forms, Access or ESOL courses, for example - should aim to develop such a style: we hope they find AWE very helpful, but they may find some of it aimed at a higher level than they currently need, or indeed understand. If you are such a student, take what seems useful, and pass over what you don't yet need.
Third, in a similar way, AWE is written with the needs of British students in mind. Those from different language communities will disagree with some of the advice given here. Notoriously, American English spells words differently. That is right in the USA. But British academics will regard it as wrong here. There are many other more subtle changes in grammar and usage, and similar variations occur in the many varieties of English that have developed, and are developing, in Australia, East Africa, West Africa, South Asia, New Zealand and all the other places in the world where English is the language in which schools deliver education.