Hi and Welcome
It's nothing to worry about.
You have probably saved the contact on your sim1 . Or the sim you are using.
You can go back to the contact listing > three dots on top right> Settings > default storage > and choose your Google account etc if you want to save your contacts to sync to your Google account.
I personally use the Google account instead of Sim as then I don't have to worry about loosing my contacts.
I hope this helps your query.
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