Extra query when lazy-loading relationship

I'm testing a simple example and can't understand why the second select * from data is needed/executed when the data is already returned by the first query. Could anybody offer any insights?

Thanks!

Route::get('product/{slug}', function ($slug) {
    $product = Product::where('slug', $slug)->with('Data')->first();
    $data = $product->data;
    return view('product');
});

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Factories\HasFactory;
use Illuminate\Database\Eloquent\Model;

class Product extends Model
{
    use HasFactory;

    public function data()
    {
        return $this->hasMany('App\Models\Data');
    }

    public function getRouteKeyName()
    {
        return 'slug';
    }
}

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Factories\HasFactory;
use Illuminate\Database\Eloquent\Model;

class Data extends Model
{
    use HasFactory;

    public function product()
    {
        return $this->belongsTo('App\Models\Product');
    }
}