A more accurate headline: "Apple fails to make enough iPhones to meet first-week demand in UK."
The iPhone 5 is extremely supply constrained at the moment so how many were sold in the UK last month would depend on how many units Apple chose to allocate to that market during that very brief initial period. Which might well have been a small number, but the number is arbitrary and not much of a reflection of demand for the phone. (Note that if they had sold more in the UK, they would have had to sell fewer somewhere else and you could write this same article about that other location instead).
The number will be meaningless until Apple gets to a point that supply is equal to demand. Either that or they should hire a polling company to poll 1,000 people to find out which phone they'd prefer.
While I'm not an Apple fan, the Android ecosystem and manufacturers still have a long way to go to compete at the same level as Apple. It's still like PCs vs. Macs out there (though getting better).
I think your parent meant "sales figure in a specific country". The 5 million thing was worldwide (or, at least, the handful of countries that offered preordering), so we don't know how many iPhones were sold in the uk.
How to compare? how many of phone X was sold in its first week and how many of phone Y was sold in its first week. Pretty simple. I'm not sure what the article has for numbers as I go by what I want when I buy a phone (or anything really) and not how many have been sold...
That's the point being made, there doesn't appear to be a source that allows any sort of comparison - how may of X or Y were sold? The article gives neither.
The iPhone 5 is extremely supply constrained at the moment so how many were sold in the UK last month would depend on how many units Apple chose to allocate to that market during that very brief initial period. Which might well have been a small number, but the number is arbitrary and not much of a reflection of demand for the phone. (Note that if they had sold more in the UK, they would have had to sell fewer somewhere else and you could write this same article about that other location instead).