Userdata array or not?

i’m using a hook to send sms to customer phone and admin phone after form submit…
In user metabox i’d stored a radio button with “allow sms notification” , so the user and admin of course, can choose if receive sms..
now.. the value stored is in array but…

    $admindata = get_userdata(1); // 1 is admin
    
    $adminallow = $admindata->user_sms[0];  //working only if set [0]
        
    $customerdata = get_userdata($author_id);
    
    $customer_allow = $customerdata ->user_sms; // work only as is

in my scenario, the admin “allow” working only if extract value from first results [0]..
but if i set the same on customer .. is not working..

so.. theorically value is “array”.. why on customer is taking it without any [0]?

Thanks