I am not really surprised.
When I was in my teens (30-35 years ago) I knew a lot of young Catholics who were attracted by the youth groups and other activities at the Evangelical churches in the area. There was definately a relativist attitude about religion among them too.
I was invited many times, usually by Catholics.
Growing up I did not attend Catholic school, I would say that 40% of my classmates in public school at any grade were Catholics. There was not enough room for us, so we were admitted on the basis of how much our parents gave to the church on Sundays.
I attended “CCD” classes, I don’t know what they call it now. Basically averything I know about the faith I learned on my own, all I retained from CCD was a few prayers I memorized.
Many of the young people I knew were “sent” to church by their parents, they had to bring a bulletin home to prove that they attended Mass.
Interestingly, now as an adult many years down the road the most virulently anti-Catholic individuals I know received their educations in Catholic school! It amazes me how little they actually know about the church they were “raised” in.
What I am trying to say with all of this is that we have been reaping the results of generation after generation of neglect and very poor catechesis. I recognize that what I saw 30 years ago was symptomatic of that.
Let’s not get confused by blaming Vatican II for all of this, these problems were widespread in the 30’s, 40’s and 50’s as well. What I experienced was business as usual, there was a sense of complacency about the whole thing because we still had the ghetto mentality.
Everyone knew that young people lost interest in the church in high school and came back to raise a family. That’s not really so true anymore and it started to change when I was coming along. We were getting converts from mixed marriages, but that was only an indicator of how far we had removed ourselves from the ghetto, it was just about the only way people were converting at the time.
The Evangelical ministries became very aggressive with our young people, and it was hard (still is) for non-Catholics to find a way in to the Catholic church, there were no obvious ways for an interested person to inquire without having to deal with all of that confusion, which can be intimidating, so it was a one way street.
So I’d say there probably are a lot of young Protestants out there whose parents were Catholic, but my guess would be that those parents simply didn’t know the Faith very well and were surrounded by Catholics that didn’t care whether they knew the faith. In other words, those former Catholics didn’t know the Faith any better than the typical Catholic in the pews today! Both groups have a lot to learn.