Quote from https://www.lawgazette.co.uk/news/veganism-judgment-doesnt-change-employment-law-expert-notes/5102613.article published by the Law Society.
"However, Barry Ross, director at specialist firm Crossland Employment Solicitors, noted that the landmark ruling does not affect the law. He said: ‘It is important to remember that this is the judgment of the first instance employment tribunal. It does not have to be followed and does not implement any change in the law. It does give employers guidance in relation to the likely treatment of ethical veganism before the employment tribunal and as such, the types of steps they should be considering for their employees and the workplace.’
So this is not a case that can set a precedent because it is too low a court and in statute law Terrorism is defined and a court cannot change what is on the face of the Act. However you make an interesting point in that if it were, in effect, a religion then it would be protected under the Human Rights Act and the Human Rights Act trumps all other legislation which is required to be compatible with it! What you highlight is why this Human Rights stuff in contrary to common sense and has just gone too far!!!