It should go without saying, but don't use your regular password for this site. There's no way they're using a unique salt for every password in their database, because otherwise it'd be impossible to match people based on the password. Without a unique salt, they're much more vulnerable to a rainbow table attack.
Why would you only ask a single question to determine best matches? And why would that question be of your password? Taking into account more information can only be better for matching people, right?
So if you also were a woman in her 30-40, fair hair, sporty, liked art and science, did not like to travel, liked spending time with friends or code - you would be a great match.
Otherwise nice password!
If they were plaintext it wouldn't need a linear search because the column could be indexed.
which seems to be a cheap (albeit honest) trick to get money out of people, so it's quite plausible that this project is simply a cheap trick to get passwords out of people.
Hopefully it comes with a followup blog post with some interesting analysis, although I'm not sure what the overlap is between "interesting" and "ethical" with a data set like this.
Hopefully it does not come with a followup blog post from somebody else who finds all the data up for sale on a darknet market...
Even if nothing at all traces it back to you, it would be easy to add every received password to a dictionary for later consultation.
But besides that, the data can be linked to you if you ever knowingly give any identifying data to another website that the attacker here has control over (or, at least, can observe). If he sets a cookie, or remembers your ip address, or your browser fingerprint, there's every chance that he might later be able to find out your real email address.
Do not give your real passwords to this site.
You could use something akin to the principle behind the Socialist millionaires problem, to compare two values without revealing them to another party.