I'm curious because I'd like to have a more portable and less destructive mining set up. I was considering a phalanx of IC2 miners. Could that be what he has in mind?
In season 4 of his SSP Let's Play you can see what he meant. He was talking about a Redpower frame quarry, as other have mentioned.
Frames are a special block that Redpower has that can be moved using a frame motor. For example, if you make a 4x4x4 cube out of frame blocks and place a motor beside it, when you send a redstone signal to the motor it will move the whole frame structure. If there are blocks touching the frame blocks those blocks will be moved as well. This functionality allows you to make a machine that will mine blocks.
In simple terms, a Redpower quarry consists of a lot of block-breaker machines that rest on frames. You send a redstone signal to the block breakers so that they mine the blocks in front of them, and then you move the whole machine forward, thus pushing the block-breakers toward new blocks. You can keep repeating this process over and over again, mining one layer of blocks each time.
This system is better than a quarry because you can mine several blocks at a time, rather than mining them one at a time like the BD quary does. Also, you can orient the machine horizontally so that it mines to the side rather than down like the BD quarry: this way, a Redpower quarry will never need to be reset, unlike the BD quarry that has to be reset when it mines all the way down to the bedrock. Last, but not least, if you design correctly, you can upgrade the Redpower quarry easily by adding new block-breakers and new frames to hold them. You could start with a small 3x3 quarry (that mines 9 blocks at a time) and end up with a huge 64x64 quarry (4096 blocks at a time), or even more. I've seen Redpower quarries that can do a mining operation every 2 seconds or so: imagine a machine that mines out 2000 blocks per second!
The downside, of course, is that it requires much more work to setup, since you have to design it and build it yourself, and you need to have the materials required to build it. And, if you build a really big one, you need to have a sorting mechanism that can handle that much work, not to mention a beefy computer to process all that activity.