As you can see in the photo below, the sign consists of 231 individual screen panels arranged in a grid 33 panels wide by 7 panels tall. If you zoom in you'll see that it's pretty easy to identify the edges of each panel:
E-ink, MPico, and Pervasive Displays have partnered to build the sign, which consists of 231 screen panels. The 7.4" screens use E-ink's Pearl screen tech and were mounted on backplanes by Pervasive Display. Each one measure 7.4" across (it's one of their stock sizes). Each panel has a screen resolution of 800x480, giving the 19 foot plus screen a combined resolution of 26,400 x 3,360 pixels.
The overall integration into a single sign, including the physical construction, electronics, and control software, is the work of Mpico. This sign is designed to be updated remotely, and according to the press release it can be updated over the internet and display either info, blank screens, or images.
E-ink is saying that this is the single largest epaper sign ever created, and when it comes to resolution they are probably correct. But if you consider simply the size then they might be wrong.
Toppan Printing Co, which I have mentioned before, has been producing for the past decade a modular sign product similar to the eWall shown above. I don't know the size of the largest screen they produced, but it's entirely possible that Toppan made a sign that was larger than 19' in size.