Earlier quoted context omitted.
IANAL but if someone makes code publicly available (for 3 years). Then isn't there an argument to be made that its reasonable to make use of it? Probably not redistribute it, but use it at least. So I'm not even sure an explicit upload license would be required.
If you leave your keys in your car for 3 years it's still illegal for me to take a joy ride in it. I don't personally believe in/support the concept of IP but in a world that does (like the US) it doesn't make sense to me that people being able to see your property for 3 years gives them the right to use it.
I'm not sure a car is the best comparison though.
How about a restaurant putting mint imperials by the cash register. Is it legal for patrons to take one?