Thanks for the nudge that Chongqing has long been a separate municipality. I want to be respectful on this point. My understanding is that Chongqing food has innovations of its own, but it’s primarily influenced by Sichuan cuisine. I certainly need to correct the above line that the analysis was restricted to things related to “Sichuan province.” Is it be appropriate to merge things together in general as “Sichuan cuisine” or is it considered more acceptable to refer to “Sichuan/Chongqing cuisine”? Ideally I’d have two separate articles, but there’s so much overlap at restaurants that I’m not sure that would make sense.
The short answer is I don’t know whether pork bone broth noodle soup (at Chonqqing Xiao Mian) is unique to Chongqing 
Nomenclature for Xiao Mian confuses me. According to a interesting read you recently posted about Xiao Mian expert “Brother Lamp”, “Xiaomian describes all varieties of the thin, wheat noodles found in Chongqing, where it is classified as a staple food, not a snack, because of its historically central role in the local diet.” He describes a few varieties, including ones resembling what Chongqing Xiao Mian cooks-- ones topped with ground meat sauce, ones topped with yellow peas that look like chickpeas, etc. Some of those dishes are not labeled by the restaurant as “xiaomian” but perhaps I should take a hint from Brother Lamp that there is a basic model, and all these other dishes are variations whether or not the characters 小麵 are listed on the menu. As for the Pork Bone Broth Noodle Soup, its name does in fact include the words xiao mian (骨湯小麵), so I wonder if they’re supplementing the basic model of Xiaomian with some pork bone broth. Do you recall if their basic model has lots of broth in it (I remember having a ton of noodles leftover, so am inclined to think not).
