array element duplicate count using convert array element to string matching the value and also get string value its possible?

function count5numbers1(arr){
 const m1 = arr.toString().match(/[5]/g);
 if (typeof m1 === 'string' || m1 instanceof String){
      return "it's not a number";
    }else if(m1 === null){
      return  0;
    }else{
      return m1.length;
    }
}
console.log(count5numbers1([1,2,5,43]));
console.log(count5numbers1([1,2,3,5]));
console.log(count5numbers1([1,2,4,2]));
console.log(count5numbers1([2,4,54,15]));
console.log(count5numbers1([1,5,55,555]));
console.log(count5numbers1([6,3,2,1]));
console.log(count5numbers1(['notnumber,its a string']));

I'm getting an answer is: [1,1,0,2,6,0,0]

But an expected answer is: [1,1,0,2,6,0, it's not a number]