The first BTC0.0025/share dividends will only be paid to the first 10,000,000 ActiveMining shares, providing public investors a priority in getting back 100% return of their investment.
What dose this mean? I'll be paid back after I buy shares from Bitfunder?

You will receive dividends on a weekly basis until your total received is .0025 BTC. Ken won't pay himself before that.
I don't think this is 100% correct. When someone buys a share, they get the remainder of the .0025 that hasn't been paid when the stock was originally issued. As of now, there has been 1 dividend payment of 0.0000183, meaning an individual who buys a share now is entitled to 0.0024817 BTC before Ken pays himself.