The context is that they're showing one metric among many and are hoping you'll draw the conclusion they want: that cars are an inefficient way to travel. It'd be interesting to see distance and time metrics added. For example, while pedestrian capacity is pretty large, the distance travelled for any specific time period is short, so people aren't walking somewhere 100 miles away.

Similarly, door-to-door travel time can vary a lot. Suburban commuter rail around here is fast, but you need to drive to the station (because suburbs are designed for cars), wait for a train, commute on the train, then find your way to your actual destination from the station you get off the train at, so that might include walking or public transit.

Obviously, any one of the options can make the most sense in a given situation, but the infographic isn't trying to show that.

I agree the graphic alone isn't super clear. I read it as the higher number being the potential capacity (such as in a particularly high-capacity system), and the lower number being the more typical capacity. Consider suburban rail, for instance. Some systems might have double-decker trains and more compact seating that allows for higher capacity, whereas some may have just single-decker trains. The double-decker system will have a higher capacity, whereas the single-decker might be more representative of what the "average" capacity of a suburban rail system might be, while the higher number might be more representative of the "potential" capacity of a suburban rail system when you really push it to its limit.