vue unexpected reactivity

I just noticed an unexpected behaviour and now I don't know if it is normal or not.

I have a component named follows and a child component named follow-list-modal

I'm passing a followList (pagination ) from follows to its child component follow-list-modal

In the follow-list-modal I store the paginated array in the variable members

Follows.vue

<template>
   <div>
         <follow-list-modal
           :follow-list="dataset">
          </follow-list-modal>
  
   </div>
</template>
<script>
export default {
props: {
   dataset: {
      type: Object,
      default: {},
    },
  },
}
</script>

FollowListModal.vue

<template>
   <div>
      <button @click="fetchMore"> More </button>
   </div>
</template>
<script>
export default {
props: {
   followList: {
      type: Object,
      default: {},
    },
data() {
    return {
      members: this.followList.data,
      dataset: this.followList,
    };
  },
methods: {
    fetchMore() {
            let nextPage = parseInt(this.dataset.current_page)  + 1;
            axios
              .get(this.dataset.path + '?page=' + nextPage)
              .then(({ data }) => this.refresh(data))
              .catch((error) => console.log(error));
           }
},
refresh(paginatedCollection) {
      this.dataset = paginatedCollection;
      this.members = this.members.concat(...paginatedCollection.data);
    },
}

When I click the button More in the follow-list-modal to get more data, I then want to append the new data to the members array.

The unexpected behaviour ( for me at least ). is that if I use push in the refresh method

this.members.push(..paginatedCollection.data); 

It appends data not only to members but also to followList which is data that comes from the parent component follows

But if I use concat instead of push, it appends data only to members variable and not to followList

this.members = this.members.concat(..paginatedCollection.data);

Is this behaviour normal ?

I don't get why the followList changes when the members variable changes, I thought that reactivity is one way.

In other words, the members changes when the followList changes, but not the other way around

P.S I don't emit any events from follow-list-modal to follows or change the data of the follows component in any way from the follow-list-modal