NICHOLAS V antipope

I was reading the vatican website and came across it saying that NICHOLAS V (1328-1330) was an antipope.

asv.vatican.va/en/visit/sig/nicoloV.htm

What did he do to cause this?

Hopefully this will be explained briefly enough at:

en.wikipedia.org/wiki/Antipope

and

en.wikipedia.org/wiki/Antipope_Nicholas_V

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