Pivot grid with remote data scenario shows expanded in header with a flat column configuration.

[MayaKirova]

Description

When data is remote and default pivot strategies are skipped with a flat config:

columns: [
        {
          memberName: "Buckets Status",
          dataType: "string",
          enabled: true,
        },
        {
          memberName: "Status",
          dataType: "string",
          enabled: true,
        },
      ],

An expander shows in the header incorrectly:

It should not show as the config defines siblings and not a parent-child relation.

• igniteui-angular version:
• browser:

Steps to reproduce

1. Open sample at: https://urldefense.proofpoint.com/v2/url?u=https-3A__codesandbox.io_p_devbox_spring-2Dbash-2Dcy9nrr&d=DwIFAw&c=euGZstcaTDllvimEN8b7jXrwqOf-v5A_CdpgnVfiiMM&r=wJ2TFK8NwqZb0nVvdmTNRL3NM1xW1Zo-jbAv6OH8pso&m=-D47jsAaQKqdGgz-m8LH6sz5C3f6fso8_RnDYMXgcWNBzFbeMXKxR7Peu5AlDsmZ&s=khU2daQr7QKgi5hbc9aPagJdg82VuNdMsfVwJDDIE4I&e
2. Observe the column headers.

Result

Expander shows but there's no hierarchy to expand/collapse.

Expected result

No expander.