nen part of the s&p/asx 300 index, page-6

It's significant because any fund, ETF or institution which offers an "index" fund needs to purchase these stocks so that the returns can appropriately mimic the ASX 300 or Allords (or whatever index). This means that there should now be buying pressure on the stock. In the US this kind of pop always happens when you get named to an index. People are obviously running the stock up in anticipation of this greater buying pressure.
It does have some significance.