A "technicality" as I see it, occurs, for example, when the Parliamentary draftsman has used slightly different words, for what is meant to be the same thing, in separate parts of the same Act. I have seen that in a Firearms Act and, it could be argued, the result was that the appellant lost. She'd have stood a slightly better chance had the intention of Parliament not been suggested in the curious choice of different wording, rather than what the intention really must have been.
Mr Freeman, "Mr Loophole", is said to get celebrities acquitted of driving offences on "technicalities". Most of his results seem to be for his powers of persuasion rather than the law being technical but the rest are down to his knowing the law better than the CPS or the police. The result is then described as "on a technicality". If the procedures required are "technical", the fact is that is how Parliament and the Minister whose department has written the Regulations, has said they must be. That Mr Freeman has gone to the trouble to study them and look for weaknesses, is reasonable enough.