Most engineers turn up at meetings with product managers with two major problems:
1. They assume they know more than everyone else. Got a guy who has had a problem for 5 years and tried 20 different solutions? The engineers will spend 10 minutes thinking about it, come up with a solution (that won't work, but they insist it will) and dismiss the problem as "trivial", and think the guy is an idiot. I've done it myself (which I'm embarrassed to admit), and I've seen it at every level from junior to Staff/Principal in companies large and small. The lack of modesty in software engineering teams is perhaps my #1 peeve with the industry. As a result, they often end up designing terrible solutions.
2. Once they understand a problem and a solution, they are frequently awful at thinking through the solution from the user perspective unless they themselves have experienced the problem. This isn't unusual, it's hard to build detailed empathy for how something should work unless you try it yourself. It can be very challenging to get buy-in for a UX or a UI from engineers without it, so sometimes it's useful to get them sat in the chair trying to do the work themselves.
I'm a TPM (former engineer and engineering manager), who has to regularly wear the "product manager" hat. I can not understate how hard it is to get engineers to read a scope document, understand it, accept that the thing needs to be built, that it needs to be built a certain way from a functional perspective, and while they have free reign on architecture and how it's built, it is not their job to rip each detail to shreds assuming the users, PMs and everyone else involved up to that point isn't a completely brainless moron.
This solution is relatively elegant. He got them to talk to users about the software they built and made them realise they were focusing on the wrong details. That's good. It doesn't mean the engineers can become product managers though.
You still need the PM to own the product long-term, and to deal with the customer relationships as the thing gets built. I will also guarantee that those engineers proposed changes the PM had to push back on because of constraints outside of the engineering team's heads (legal, compliance, needed by customer X, and so on).
Edit: read down into the thread, and this company doesn't have product managers. So he's just hoping engineers can figure it out. Fair enough, the only way to develop that muscle though is to get them in front of customers regularly.