Might be the photo, but it looks to me like top is vanilla cookie with choc-chip, while bottom is chocolate cookie with choc-chip, making it "double" chocolate.
Definitely could be clearer, but I don't think they're making the claim you think they are.
I would assume double chocolate means chocolate dough and chocolate chips. Double in essence, not in quantity. And 40% is referring to how many chocolate chips are in the dough.
Only way to know is if OP shows the ingredients. That brand of frozen cookie dough, however, uses dark chocolate chips for the double and milk for the standard, so it's unlikely.
I my (extensive) cookie experience, double chocolate usually means the same amount of chips, but the dough part is also chocolate flavoured. Hard to tell in this instance, but the "double" cookies may be a shade darker.
In cookie lingo, double chocolate means the cookie dough is chocolate flavoured as well as having choc chips. Triple chocolate means the chocolate dough with choc chips also has a chocolate coating on the bottom.
No... chocolate coating is usually referred to as "dipped." Triple chocolate cookies are usually (but not always) chocolate dough with chocolate and white chocolate chips.
Could also be two different types of chocolate (adding up to the same amount overall). Both packages are 225g, so the overall weight is certainly not doubled.