They had to go to EU tender because they went out to tender.
If you don't put them out to tender WTO rules don't apply.
Which is why before the current insanity most NHs work was not carreid out under tendered contracts.
Also we have defence tenders going abroad because the Government chose to make them go abroad.
There is nothing in WTO rules that requires this.
For example, numerous countries in the world maintain state arsenal systems, even those have fallen out of vogue in the West.
Even if WTO rules did require it, the WTO is a dead letter anyway.