Category exposure and entity exposure answer different questions. A risk category such as money laundering classifies the risk, so one payment can appear under several categories at once and category amounts do not add up. Entity exposure collects the paths to one entity across all categories and lets each shared transfer carry its recorded value only once.
Because the measure uses aggregate transfer values rather than transaction order, it shows how much could have moved, not which coins actually did; answering that takes fund tracing. Amounts for different entities can share transfers, so they are not added into a single total either.