I redownloaded Snapchat today on my degoogled phone since my friends use it all the time now and I’ve also seen that it somehow got all of my contacts. Turns out that it uploaded my contacts to their cloud without me clearly telling that when I first signed up.

To check if your contacts are in cloud: Go to your profile > Open “Settings” by tapping the cogwheel > Under “Account Actions”, select “Contact syncing” > Tap “See contacts shared with Snapchat”. You can delete your contacts there too, I just did that. If you have an Android phone, I’d recommend you to patch your app with something like ReVanced to minimize data collection.