It's by far not limited to only open source projects. There are many situations where some fault, no matter how small or irrelevant, has to be found in order to sate the ego of the person doing the review or consideration of a problem or piece of work.

I don't think it's limited to open source project either. But open source projects are unusual in that often even when commit rights etc. are controlled, being able to opine on submitted patches is open, and a way of building social status within the project. And while that often works well, it also does attract people who may even mean well, but will be overly critical because it's their way of feeling they're contributing.

In most corporate projects, odds are you're dealing with a much smaller pool of reviewers.