Svelte 5 reactive store methods

The below code is working as it should, I'm just trying to gain a better understanding of why.

How is the getCurrentElement method of TestState reactive without the use of $derived()? Are store methods that make use of state reactive by default?

Im using svelte@5.0.0-next.217

test-store.svelte.ts

import { getContext, setContext } from 'svelte';class TestState {  elements = [    {      id: 'hghxt',      name: 'Give',    },    {      id: 'vhtl9',      name: 'Connection',    },    {      id: '5n0t0',      name: 'Take notice',    },    {      id: 'xlfba',      name: 'Keep learning',    },    {      id: '1f3z2',      name: 'Be active',    },  ];  #currentElementId = $state<string>();  getCurrentElement() {    return this.elements.find(element => element.id === this.#currentElementId);  }  setCurrentElement(id: string) {    if (!this.elements.some(element => element.id === id)) return;    this.#currentElementId = id;  }}const TEST_STORE_KEY = Symbol('TEST_STORE');export function setTestState() {  return setContext(TEST_STORE_KEY, new TestState());}export function getTestState() {  return getContext<ReturnType<typeof setTestState>>(TEST_STORE_KEY);}

TestComponent.svelte

<script lang="ts">  import { getTestState } from '$lib/stores/test-store.svelte';  // initialised at +page.svelte  const testState = getTestState();</script>{#each testState.elements as { name, id }}<button     class:bg-yellow={testState.getCurrentElement()?.id === id}     onclick={() => testState.setCurrentElement(id)}>    {name}</button>{/each}