I’m skeptical this was intentional. Dirt doesn’t look disturbed, and the dirt here gets lumpy when dug or like powder when it’s moved around this time of year. It looks just as buried and the dirt compacted as the rock right next to it. I’ve found old pocket knives before (even when I was in Boy Scouts) and they were in better condition than what I’m seeing here. And I still use one of them after a quick restore.
That glass has been there a long time, and is mostly likely is from kids or fishermen drinking.
When we cut the new trail by Middlebush in January there were tons of beer bottles right under the brush we were moving, broken and whole. I could easily see a knife being dropped, getting covered at some point, and uncovered just due to the crappy condition of that trail. Just my $0.02.