Answer is that, when you download update in your phone , you will get delta update or patch and when you use smart switch in Windows, you will receive full image of firmware.
It is recommended to do update using smart switch when you get major update, like when you update from android 10 to 11
I updated major OS ONE UI 3.0 and ONE UI 3.1 through Smart Switch and now May security updated through Smart Switch, the difference is Smart Switch download the whole firmware whil OTA gives only the addition update
