There are numerous explanations for this occurrence. You'll notice that the text doesn't identify it as a miracle. He didn’t pray; it doesn’t mention the Lord doing anything; there is no outburst of praise afterward. It may be a miracle, but maybe not.

1. He probed the muddy waters with a long pole until he pushed the object to within the man’s reach. And thus, it "floated." (Gray; Ellicott; Von Gerlach)
2. He cut a new ax handle, poked it into the eye of the ax, and when the handle entered it, the ax head floated together with its handle. (Qimchi; Thenins)
3. A miracle. (Benson; Jamieson-Fausset-Brown; Gill; Cambridge Bible commentary; Pulpit Commentary; Geneva Study Bible; E.W. Bullinger; Rabbi Elchanan Samet)

Robert Bowman makes the comments that...

1. It is consistent with the other miracles attributed in 1 & 2 Kings to the agency of Elijah and Elisha.
2. It is consistent with other miracles performed in the Pentateuch.
3. It reverberates with some of the events reported in the Gospels.

I think the mention of the "borrowed" ax is that it is for Elisha an act of compassion, much like Jesus's turning water to wine, where they've run out of wine (a social disaster) and Mary prompts Jesus to intervene (Jn. 2.3-5).

For reference:

2 Kings 6:1-7

Now the sons of the prophets said to Elisha, “See, the place where we dwell under your charge is too small us. Let us go to the Jordan and each of us get there a log, and let us make a place for us to dwell there.” And he answered, “Go.” Then one of them said, “Be pleased to go with your servants.” And he answered, “I will go.” So he went with them. And when they came to the Jordan, they cut down trees. But as one was felling a log, his axe head fell into the water, and he cried out, “Alas, my master! It was borrowed.” Then the man of God said, “Where did it fall?” When he showed him the place, he cut off a stick and threw it in there and made the iron float. And he said, “Take it up.” So he reached out his hand and took it.

What is the meaning of this story/scene?

One possible parallel I see is with Moses in Exodus 15:25 where he throws the log into the bitter water and it becomes sweet. It’s the same Hebrew word ( עֵץ֙ ) used for log/stick in both passages, but I don’t know what to make of that, if anything.

I also don’t understand the meaning of the axe head being “borrowed”, which seems to be the word used in most translations.