I agree with most of Masaken's comments. Speaking exams for Beginners and Continuers language courses are intended to assess students according to their ability to discuss a range of topics in the form of a conversation with their examiner for 5 minutes and 10 minutes respectively. The exams usually begin with simple questions that allow for the conversation to be initiated and developed, after which the examiner can change the focus of the conversation to allow the student to speak about different topics.
If a student demonstrates a high level of fluency in the target language (where the standards that are considered high are lower in Beginners courses than those in Continuers courses), it is normal for the examiner to ask both follow-up questions and new questions that change the focus of the conversation in order to provide the student with the opportunity to maintain this standard for the remainder of the exam. On the other hand, if a student is unable to provide sophisticated responses, then the examiner will not be able to develop and change the focus of the conversation as intended (doing so would be pointless anyway if the student cannot further develop their answers) and will instead opt for simpler questions.
In terms of personal experience, while I obviously did not have any issues during my speaking exam since I am a native speaker, I can definitely understand if other students may have struggled a bit to answer questions of the same difficulty. This is therefore a reminder of the importance of ensuring that language students (this applies to all levels, not just Beginners and Continuers) maximise their preparations for their speaking exams.
This notion of subjectivity does not apply to Extension language courses, where all students have a choice of answering one of two questions in monologue form.