Amount of organic keywords and search traffic aren't directly proportional. There can be several reasons for the increased amount of keywords and the decreased search traffic numbers:
there is a keyword A that bids for $1, has 1000 monthly search volume and gives 500 monthly visits to the site. The traffic value is $500.
keywords B and C that bid for $5, have 10000 monthly search volume each and give 50 monthly visits to the site each. The traffic value given by each keyword is $250.
If the site originally ranked for keyword A, but then lost that ranking and started ranking for B and C instead:
the number of keywords they rank for became one more than it was (the website lost ranking for keyword A, but got two new keywords B & C, delta is +1 new keyword);
the search traffic dropped by 400 visits (-500 visits from lost keyword A, +100 visits from keywords B & C, delta is -400);
the traffic value remained the same (lost traffic value of keyword A $500 + gained traffic value of keywords B + C $500 ).
2. If there's a change in search volume of keywords your website is ranking for, traffic will change as well, whereas amount of keywords remains the same.
3. Since for traffic calculation we consider keyword's ranking position and our estimated CTR for that position, if CTR curve for a keyword changes, it will lead to traffic change as well.
4. Appearance or disappearance of ads in search results.
5. Appearance or disappearance of sitelinks in search results.