I only know a couple directly but I know more indirectly over in the factory- minimum week and a half and thats if it really was mild. I know one who is still rough after 3 weeks and that was "mild".
Boris clearly did have symptoms otherwise he wouldn't have been tested, he wasn't asymptomatic (unless he was lying). So either he was totally asymptomatic and a test was done as a precaution & was positive (in which case there's a lie as we were told he had reported symptoms), or he is symptomatic and is a miracle of medical science, and can come out of hiding in 3 days when the rest of planet earth is told 14 days is the isolation period.
There is no shock or surprise here, just more inconsistencies & bullshit flying around.
But as has been said it largely depends on how much of the virus you pick up on transmission, but then depends on individual factors like the strength of the immune system etc..
If it's only a very small amount then your body will notice it and start fighting it when it hasn't got that much of it to deal with, and also means it takes longer for the virus to replicate to a level that would overwhlem your immune system. Thus you end up with less of the virus in your system and making your symptoms milder and your recovery likely to be quicker.
If you get a massive dose (ie someone sneezes on you) then your body has a large amount to deal with very quickly and all that will replicate exponentally in your body making the job for your immune system much more difficult. As it struggles to cope it either goes into overdrive and causes damage or eventually is overwhelmed and gives up.
Think of it like the difference in infection rate of flu to coronavirus of 1.4 to 3 and the difference it makes in how many people are infected. It's the same principle of exponential growth, just going on inside your body. It's the principle behind active vaccines.