OK, OK ... let's get a few things straight ....
First ... this is NOT my work. Or, at least, 99% not my work!
I apologize for the pic ... there was not room in front of the panel for me (due to pipes) .... I took the pic by holding my arm out, pushing the button, and hoping. This was in a basement, lighting was poor .... and, frankly, I had not noticed that green hose / wire / cable / whatever it is.
Looking at the original, unedited picture, it appears that green thing enters a 4" pipe in the foundation. Everything at that point is well below the frost line, so I can't imagine what it may be - or even say that it enters the panel.
Someone else mounted this (sub) panel in this 1920's house. I was called because the oil furnace - located behind me as I took the pic) wasn't working. In order to fix that problem, one thing I did was install that Romex you see - the connector looks new, because it is! The cable is anchored out of view.
KO's on the top were either taken, or obstructed. I used the one you see ( and not one higher up) because it had no wires, etc., behind it inside the box. And, as you might guess, I had to contort myself somewhat to even do that.
(1920 house, sundry handyman work, heat out and it's 7F in this rental property .... this is no time to try to fix everything that might be wrong .... just enough to try to make YOUR part OK).
Lighting was poor; until I edited this pic, I did not realize that the cover was also notched a bit too much, and that there actually is an opening into the bottom of the panel.
I'll have another thread - soon - about this job. Maybe two! For this thread, though, .... well, that pic can really challenge our understanding of 'neat' and 'workmanlike!'