No it doesn't. Your password has as much entropy as it has, and no more.

If you want to follow that train of thought to its logical conclusion, your attacker not only doesn't know the length of the password, they don't know what character sets make up the password either, and so you could claim that a 4-character numeric password is equally secure to a 64-character Unicode password. In fact by inductive reasoning 4-digit password could be said to have pretty much any finite amount of entropy, because how does the attacker know that it's not actually length N+1?

Yes, the attacker not knowing exactly what the password class is (words/character set/length) does help somewhat in a practical sense. But it doesn't "change the math" at all, if you have 3000 symbols (words) and your password is 4 of them then you have 3000^4 possible passwords. You don't get to count passwords that are not in your password class as part of your entropy.

I didn't mean math in general, I meant the math used in the post I was responding to, which had some unfounded assumptions. I can make assumptions too with vastly different outcomes, I'm sure that 10 random unrelated words are more secure than 10 random unrelated characters.