Test, Track & Trace Anomalies

My son unwittingly had contact with somebody with Covid last Thursday. He found out Friday that she had symptoms so was being tested and immediately went into isolation in his room. Knowing he wasn't allowed an NHS test without symptoms, he ordered a private test yesterday. The Government website said he had to isolate until he got a negative result so he was keen to at least be able to come out his room to be with his flatmates.
Today he has received an email from Track and Trace saying that he must isolate for 14 days until 30th September because the girl got a positive result yesterday even if he gets a negative result from his test! Now, even if you take into account the fact that it may take up to 14 days for symptoms to show, there has been no allowance whatsoever for 6 days he was already self isolating to avoid the spread. By the time he has finished, he would have been isolating for nearly 3 weeks.
For him, this is not going to be a huge problem because he isn't currently working so there is no loss of income and the only things he has to be concerned about is boredom and loneliness. However, if you were a worker without paid sick leave, this could leave you very broke.
I think that the advice between the GOVT website and T&T is somewhat contradictory although to be fair, if you look hard enough, down the bottom of the page, there is an ambiguous link to T&T which tells you their advice supersedes earlier advice on the page but I wonder how many people read the top advice and then don't read further. AIBU to think that alongside the advice about negative results there should be a warning to use the Track and Trace page rather than hiding that!
Am I also being unreasonable to expect the companies who sell this test to be explicit about not being able to stop isolating even if you test negative.
And finally, AIBU to expect the Track and Trace people to at least allow for the date you last had contact with the Covid carrier to be the first date.
If you want people to be sensible about isolating as soon as you are aware that you might have been infected, there has to be some incentive.
My only consolation in all of this, including the Birthday money my son has wasted on a test, is that he will hopefully be far more careful in the future. There have been times when I feel he has been more blasé than I would have liked him to be. On the other hand I was relieved to hear him say that he was going to isolate immediately until his friend got the all clear because he didn't want to be a spreader.