That WB statement is 90% marketing BS, an effort to differentiate the CDi from the rest of the range.
Condensing occurs when the heat exchanger, or a portion of it, is below the dewpoint of the water vapour in the gas combustion products. When this happens, the water vapour condenses and gives up a considerable amount of heat to the exchanger. Clearly the heat exchanger is more or less at the temperature of the water flowing through it. Typically this water will be at a particular temperature entering the heat exchanger and will be hotter when it leaves, frequently starting out below the dewpoint and leaving above it. Because of this and because not all the water vapour will be able to condense out without a very long pass over a cold heat exchanger, all boilers only partially condense if they condense at all. That is, they only extract a portion of the available energy from the water vapour.
So the statements by WB (as well as by many other manufacturers) that their CDi boilers "fully condense" is meaningless and inaccurate. Similarly the inference that the other boilers in the range do not condense in DHW water mode is also meaningless and inaccurate. Both partially condense. Although incoming water much colder than the dewpoint, it doesn't come into contact with the heat exchanger. In all WB combis (and most other domestic boilers), the cold water passes through a secondary heat exchanger where it is heated by water flowing round the inside of the boiler through the main heat exchanger. Differences in the flow rate of this water and the size of the main heat exchanger (much bigger in CDis) mean that the CDi boilers are able to condense considerably more water vapour than the other models. The controls are also set to limit the maximum temperature of supplied hot water to 60C so that water flowing into the main heat exchanger is always below the dewpoint.