From the article : "In her re-election campaign, Mayor Anne Hidalgo says that every Paris resident should be able to meet their essential needs within a short walk or bike ride."
"Paris" is defined as Paris intra-muros + the Boulogne and Vincenne parks, which are limited in space and was saturated long time ago. You are a "Paris resident" if you live inside of the City of Paris (the green line of the plot).
The chart is showing "Aire urbaine" and "Unité urbaine" which are another way to draw geographical limits and are only used for statistical purposes, and they include the "Region of Paris", or "Ile de France". Obviously, the region is expanding like any other capital's region in the world, so that plot exactly shows nothing.
The sentence "For most practical purposes Paris is a 10 million inhabitants city" is fake news. People living inside of the City of Paris are asking to be able to use bikes or other transport means, but all the cars coming from outside of Paris everyday are making it difficult.
Stop confusing the Region of Paris and the City of Paris. People living inside the City of Paris (the Parisians) have right to elect a mayor who will defend them. If you live in one of the adjacent cities, go elect a mayor that will locally improve your quality of life, but (real) Parisians are sick of the traffic inside their city and no other city has right to decide for them.