I was told there is a server technology that allows user to seek to a part of video that has not been loaded yet even if I am using progressive download, not true streaming.
What technology is it?
There are multiple ways to handle what you describe, for example: http://h264.code-shop.com/trac#Timeshiftingseek or http://stream.xmoov.com/.
Obviously this won't be able to play data you didn't receive. It's a standard progressive HTTP download where the video file is "cut" on demand server sided.