First off, I need to clarify. I grew up referring to sieves as strainers. So where I have written strainer it should have said sieve.
Sieves come in various shapes and I see them most frequently having a bowl-shaped base.
Chinois are conical so you can use a wooden pestle to push particles through. Chinois, in my experience, are built stronger than most sieves. The mesh might be double layered. Or there may be solid metal panels alternating with mesh panels.
We are at the point where so many people write about food and cooking. Their backgrounds are so varied. Which has caused much blurring of the meaning of terms that used to be clearly defined. I’m not professionally trained so I may have absorbed misinformation. But based on reading and the way my cooking professional friends referred/used the items I’ve come to understand them in this way.