Looking at the article, it's unclear if it is retailer orders or pre-orders. Either way, it is a good first run.
The article says something like "for a series that normally sells a million in Japan, the number of orders seems little, but the biggest selling title in Japan for the PS3 right now is Gundam Musou with 290,000 units, so 300k is good."
Pre-order numbers haven't exactly been on the money lately. First were reports that God of War 2 had over a million pre-orders, but it "only" sold about 800,000 in it's first week (I say "only" with quotes because 800k is still huge). Then the story about 4 million pre-orders for Halo 3.
So, I'd say, there's a good chance this will sell between 200k-300k in it's first week, which would be fantastic for the PS3, and it would become the fastest selling PS3 game in Japan.
July is still a ways off, so if we don't hear of the pre-orders going above 300k, then maybe it was retailer orders.