Taraveling with my polish partners to Uk as no eu partner permit holder

Hi this is for my frind who is living in Portugal with polish partner my frind is Pakistani national and he just recently got the RC temparry EU card on basssis of as Eu living partner it’s given for 5yers , he recently taravel to Poland with her and he had no issue flying out, now they are flying to UK from pourtgal but on air port Esye jet airline didn’t allowed them to fly out and they are not giving any thing in writing ,
My question is he was flying with his partner to visit UK
Why he has been stopped ?
Please can some one advise

Also just to add he got temporary RC card for five yers under Artical 15 as per pourtugal EU law

I'm going through easy jet in 2 weeks with same card
any suggestion please