Philosophical truths are not the same as objectively shared truths like the capital cities of nations and the time of day. Of course we would not say 1 + 1 is considered to be true, but we must say that Kant considered moral truths to be definite, permanent and objective and in that sense, I believe your student was correct.

You even said so in your own article, not all philosophers agree and there are many different views on ethics, morals, truth and therefore it is kinda relativistic, naturally so.