The USCCB is not the writer of the NAB bible, nor it’s footnotes. Those are written by independent theologians, and scholars, and are not binding church teaching in and of themselves. The USCCB merely hosts a copy of the NAB bible.
There is a very distinct difference between friendly love, and the highest form of love, Agape. A person who is merely a friend, doesn’t lay their life down for people they are merely friends with ; let alone for their enemies.
Romans 5:10 Indeed, if, while we were enemies, we were reconciled to God through the death of his Son, how much more, once reconciled, will we be saved by his life.
Read what St. Paul says in context, for he talks specifically about Agape in Romans chapter 5, where it says “Love” in English.
If you trace out the NAB’s footnotes for John and the sheep, you’ll notice it goes indirectly to Romans 5, but the theologian does not reflect of the fact that enemies are not friends of any worth. So, when they glibly say “with apparently no difference in meaning” – they are talking about superficial appearances, and not the reality.
It’s not a well thought out footnote.
John records just a few sentence away from the note on ‘laying life down for a friend’ an incident where Jesus says, “I no longer call you servants, but friends”
Their friendship was a rite of passage from a lower, or lesser office to a greater one.
For a friend knows what the Father is about, and the plan has been revealed to them.
Just so when Jesus says “Philea”, “friend”, that implies that Jesus is saying:
"Peter, do you know what the plan is? Feed my sheep! "
In shepherding, there are three stages of growth – and generally, different people are assigned to sheep of different ages. But in the passage where Jesus talks to Peter, there are only two kinds explicitly mentioned. Because there are three sayings, though, it is traditional to understand all three stages of sheep being Peter’s purview. He is, the ‘universal’ shepherd.
However, I find this especially interesting, for the denials were also structured as two, vs. three in Peter’s account (Mark is Peter’s scribe); “before the cock crows twice you will deny me thrice.” ( Mark 14:72 ).
So, I doubt that it is just a facet of the Greek language that there aren’t three distinct words for sheep, which causes there to be two mentions of one kind and only one of the other. The structure of the saying appears to be quite deliberately set up as two of one kind of thing, and one of another.