440ml is a UK variant. No one has a confirmed explanation for its existence alongside 500ml, but it's been around for decades.
However 440ml of water would be 0.44kg which is just under one pound imperial weight (0.45kg). Presumably the fluid plus the aluminium can would weigh about 1lb which may explain the odd volume measure (given transport costs are often by weight and possibly even how customs costs may have used to work?).
In a pub yes. But in cans both 500ml and 440ml are common sizes and have been for a long time. Pint sized cans are sometimes available but are much less common and I’m not sure I’ve ever seen them in a big multipack