‘And Abram passed through the land to the place of Shechem, to the oak of Moreh. And the Canaanite was then in the land.' The arrival at Shechem (a very ancient city) is mentioned because it is here that Abram will have his first meeting with Yahweh in the land.
“The oak of Moreh” may be intended to indicate an oak forest (compare Genesis 13:18 and Deuteronomy 11:30). Alternately it may refer to a particularly famous oak, possibly with religious connotations. Indeed the particular oak may have been called that precisely because it was there that God met Abram, and there that he built the first altar to Yahweh (Genesis 12:7 compare Genesis 35:4; Joshua 24:6).
Shechem was under the control of the Hivites (Genesis 33:18 to Genesis 34:2). This is drawn to our attention by the phrase that ‘the Canaanite was then in the land'. Hivites were seen as ‘Canaanites', and had associations with Lebanon (Genesis 10:17; Judges 3:3; 2 Samuel 24:7). Thus ‘the Canaanite was then in the land' is probably not a phrase written long after, looking back, but is one pointing out that by this time Shechem was Canaanite. It had previously not been so. The presence of people called Canaanites in the area is mentioned for the first time around this time in external documents. Thus the writer has an intimate knowledge of the recent history of Canaan.
Some take the other view in which case we have a typical explanatory note of the kind often introduced into records as an updating comment, without changing the narrative. But the former explanation is more likely. Whichever way it is it cannot be used to date the whole record.