What causes Android to launch an Activity with the URI of format "custom://12345678"

Question

For analytics, I am gathering data on what URL/URI causes my app to be launched.

When I inspect the intent and the data to determine the URI that started it, using:

getIntent().getData()

the URI is often of the format "custom://123456789" (many different large numbers show up)

I would like to understand what causes it to be launched with that Uri format, to know if I can safely filter those cases out from stats.

As requested: Here is the activity entry in manifest with intent filter to catch starting from the Launcher, or from clicking on a URL from my domain.

    <activity
            android:name=".ui.activity.MainActivity"
            android:clearTaskOnLaunch="true"
            android:configChanges="locale|orientation|keyboardHidden|screenSize"
            android:label="@string/app_name"
            android:launchMode="singleTask">
        <intent-filter>
            <action android:name="android.intent.action.MAIN"/>
            <category android:name="android.intent.category.LAUNCHER"/>
        </intent-filter>

    <!-- Capture the opening of the app via a link to app.tuenti.com -->
    <intent-filter>
        <action android:name="android.intent.action.VIEW"/>
        <category android:name="android.intent.category.DEFAULT"/>
        <category android:name="android.intent.category.BROWSABLE"/>
        <data android:scheme="http" android:host="mydomain.com"/>
        <data android:scheme="https" android:host="mydomain.com"/>
    </intent-filter>
</activity>