The first sentence of the cited article reads:
A man has admitted sharing a grossly offensive video of a cardboard model of Grenfell Tower being burned on a bonfire.
Section 127 of the Communications Act 2003 seems to be the most relevant offence:
(1)A person is guilty of an offence if he—
(a)sends by means of a public electronic communications network a message or other matter that is grossly offensive...
However, there's also similar offence under section 1 of the Malicious Communications Act 1988:
(1)Any person who sends to another person—
(a)a letter, electronic communication or article of any description which conveys—
- (i)a message which is indecent or grossly offensive;
(b) [...]
is guilty of an offence if his purpose, or one of his purposes, in sending it is that it should, so far as falling within paragraph (a) or (b) above, cause distress or anxiety to the recipient or to any other person to whom he intends that it or its contents or nature should be communicated...
Both charges seem available on the information provided, so it was up to the Crown Prosecution Service to pick the most likely to succeed.
sending "grossly offensive" material
lead me to this jmw.co.uk/services-for-business/business-crime/…