Perhaps I am reading that article incorrectly but Thomas Mair was not charged with terriorist offences he was charged with murder and found guilty.
Yes, I believe that is correct, but what difference does the offence he was charged and convicted of make? The case was certainly treated as a terrorist one:
”At a bail hearing on 20 June, the judge remanded Mair in custody until a hearing to be held "under terrorism-related protocols". At the next hearing on 23 June, the judge said the case would be handled as part of "the terrorism case management list", on which cases related to terrorism as defined by the Terrorism Act 2000 are placed”
I believe Lee Rigby’s killers were also convicted of murder rather than a specifically terrorist offence.