WeChat, taobao, alipay, amap they all do this. Go to watch /pictures on your android with a file manager. You will notice some folders called .gs0 .gs3 and so on.
Inside there are dummy images with tracking data. They do like this because apps on Android don't need an extra permission to drop "images" on /pictures
Those folders are not shown by default because normal file managers on Android hide any file with the name that starts with a dot.
And those dummy images aren't shown in photo galleries also because of another file that's dropped in those folders, .nomedia
You also never saw the ads on the taobao splash screen???? Did you ever opened that app? Not to mention that phone permission is mandatory to use that app for some reason. (And can't do any search until you register your phone number with SMS verification)
Other Chinese apps with ads on the splash screen is Huawei store, mijia, amap
And the Chinese customs app also requires an insane amount of permissions, never gave my European phone number, but a week after entering the country I got a phone call from +8621962110 - who gave them the number? (Don't know what that call was about because answering a phone call in roaming is 2 euro per minute, but from some search on Baidu it looks like it's some robocall from the Chinese police)