But even if we take your view of which definition applies, your argument presumes that this kind discrimination is inherently wrong, at all times and in all places. Governments discriminate in a number of ways, all the time. They do it through licensing requirements, or age limits, or otherwise determining that certain groups qualify or do not qualify for certain services. It also conflates the sort of discrimination based on a person's inherent properties (e.g. skin colour, disabilities) which the law rightly prohibits with decisions based around the choices individuals make. And, for all but a very small number in the UK, the decision about whether or not to be vaccinated is a choice.
Even where I disagree with them, I've time for arguments based on efficacy or practicality. Those that try to co-opt the arguments of discrimination to portray those who are affected by these measures as in some way put upon, however, I regard as beyond the pale. And, as we saw with many of those who voted "No" last night but supported government legislation that really is discriminatory, they frequently accompany deep hypocrisy.