http://www.legislation.gov.uk/...
"13 Abstracting of electricity.
A person who dishonestly uses without due authority, or dishonestly causes to be wasted or diverted, any electricity shall on conviction on indictment be liable to imprisonment for a term not exceeding five years."
So yes, the language is precisely correct.
Technically he has also committed a criminal offence.
However, PCSOs (which are sometimes known unaffectionately at "plastic policemen" are non warranted police officers with very limited powers. Most of their arresting powers are actually the same as those available to any citizen (aka "citizens arrest") and have very limited conditions of applicability. PCSOs do have some additional powers specially granted:
https://en.wikipedia.org/wiki/...
However, they are a modern invention and of considerably lower status, both legally and in the public perception compared to the more traditional volunteer role of "Special Constable" - https://en.wikipedia.org/wiki/...
The problem here is that PCSOs generally lack common sense and seem to be power-happy. Unfortunately their warranted colleagues feel some obligation to back them up, rather than telling them to grow up, as might be applicable in cases like this.
Unfortunately for the artist, even through he has been de-arrested, he now probably no longer qualifies for the visa waiver programme for entry to the USA as the US notion of arrest is somewhat different to the English notion and the USA as far as I know does not have a concept of "de-arrest".
So actual harm has been done. No wonder the public perception of the police is falling like a lead balloon.