Can't understand a deduplication code in BigQuery

Question

I'm new to SQL, and i got this piece of code, inspired by this post Delete duplicate rows from a BigQuery table

I ran the code, and understood that it deduplicates my table, but i'm not sure how.

The code is the one that follows

WITH product_query AS(
  SELECT
  DISTINCT
  v2ProductName,
  productSKU
  FROM `data-to-insights.ecommerce.all_sessions_raw`
  WHERE v2ProductName IS NOT NULL
)
SELECT k.* FROM (
  #aggregate the products into an array and only take 1 result
  SELECT ARRAY_AGG (x LIMIT 1)[OFFSET(0)] k
  FROM product_query x
  GROUP BY productSKU
)

I think i got the first part, but, starting from "SELECT k.*"... i'm not sure what am i looking at. What the "k" and the "x" are supposed to mean? And what is the OFFSET function?