Hey, everyone! Sorry I didn't come back sooner, but I was traveling for work. You are correct that it is catchfly/silene. I think I grew it years ago, and maybe had one solitary plant come up in that bed last year with some other plants. That's all it would have taken.
We had water line repair work done, so it's possible that when the trench was dug and everything was upset, some seed managed to find its way over to that area. I don't know how long it remains viable.
