Yes and no.
I'm listening to a little more of the audio now, and the articulation is somewhat hit-and-miss. He has the voice of someone who's sixteen years old, and there's not a great depth of vocabulary but it could feel to an adult that it's not that much different from talking to a rather indifferent teen who has a 'strop on' (sorry if that doesn't translate into US/International English. The problem is that this isn't a kid with a strop on, this is his highest level of interaction, and it's far, far easier for him when he's talking about things he's been personally involved in, or small passages of conversations he's overheard....outside of those things he gets very slow, lots of pauses, fractions of sentences or no answer at all. It's awkward with it being audio-only to imagine if he's just sitting there or if he might shake or nod his head at times, there's no way to know, it has to be inferred from the officer's response. The officer is finding it difficult to elicit information, but he seems to be doing a reasonable job of keeping it sounding like a friendly chat and working around these pauses and places where Brendan doesn't really know the answer... (paraphrasing) "Do you remember which day *advertiser censored* happened? Thursday? Which Thursday, this one coming up or last week? Last week, okay, that's fine." or "What were you doing that afternoon? Playing video games on the Playstation...do you remember which game? [response from Brendan, slightly bitty, but clear enough that it was a relatively new game] Oh, so when was that bought? [Brendan doesn't remember exactly] Ohh, okay that's fine."
There's nothing hostile, it sounds a little like chatting with a younger child, maybe 8 to 10 years old, but with the deeper voice of a sixteen-year old. He doesn't seem to like saying anything when he's not certain of the answer.
The problem is that people tend to make assumptions about other people based on their own brain patterns and experiences. Someone like Brendan is hard for them to comprehend and empathize with his thinking and speech patterns, especially when he goes from articulating fairly well about a video game to not being able to answer the question of when it was bought. People tend to insert themselves into someone else's personality (if that was me, I'd be lying if I acted like that). And these guys admitted that when they were interacting with him they were seeing all the interviews they'd ever done with numerous other criminals and really interpolating other people's actions/reactions/speech/motivations onto Brendan. This is what people do, they ascribe motivations based on their past experiences not on the person's past experiences.
When you get a person with a 'delicate' demeanor and you start vocalizing these ascribed motivations to them, they're often not able to fight, they just accept them. ["You're stupid! Why did you do that thing?" "Because I'm stupid."] So in many ways the individual feeds back these ascribed motivations instead of attempting to explain what's really going on in their head when the other person has already made up their mind, and wouldn't have a hope of understanding anyway.
But I don't think the officers were trying to coerce answers, I think they genuinely couldn't understand why he would stop articulating and not give them the answers they wanted [unless they pushed hard on him]. Sure, this is 'wrong', and definitely not the right way to question a person like Brendan (it could have the same effect on people who are older and with much higher IQ and no learning difficulty, especially if they've experienced this kind of emotional bullying at some point in their life) but I don't think they were doing it on purpose...they just wanted the answers and it was their job to get the answers that made a rational narrative of what happened to the victim of a horrific murder.