Sentence Correction

In MGMAT SC under Verb tense, Mood and Voice Strategy - Past Perfect

The sentence goes like this -

The band U2 WAS just one of many new groups on the rock music scene in the early 1980's, but less than ten years later, U2 HAD fully ECLIPSED its early rivals in the pantheon of popular music.

According to the rule the earlier past moment will be in the past perfect and later past moment will be in the simple past.

But here the action U2 new in the industry is prior to becoming popular which happen 10 years later. So why the past perfect is used in the later past action whereas it should have been used in the earlier past action?