Ion engines do use fuel. The wiki page you linked to even lists the propellant types (https://en.wikipedia.org/wiki/Ion_thrus…) for example the Xenon Ion Propulsion System is used in many commercial satellites.

It is true that the visualization doesn’t show the most used emoji. But I disagree with the “hardly sound data science” statement. The most used emoji is likely the same in each state and uninformative :) . Differential expression (very appropriately named in this case) is valid data science.