It's only hard to tell if you don't talk to the developers who were working in the late 90s.
I think you mean "working ON it". Talking to developers as a broad group from that time wouldn't necessarily produce any useful information.
The person you replied to was himself a developer working in the late 90s. During the late 90s, I talked to a lot of developers, but only a small percentage of them were on Y2K jobs.
So while we were -aware- of the Y2K issue, it didn't impact any of us in a concrete fashion. We would talk about people we knew on Y2K projects, which were mostly mission critical legacy systems.
So it's not inconceivable for devs in the 90s to have only cursory awareness of the -real- issues that the people who worked on Y2K projects were facing and solved.
For context, most of the devs I worked with at that time finished their CS degrees within the previous 10 years, and were not legacy systems programmers. Doing 2 digit years was inconceivable to them.