At the end your program gives (12-18) the score: -7.
That means: surely draw, and not probable draw. Am I right?
No. Unlike database win or database loss scores, which are conclusive indications of those results, database draw scores are not necessarily conclusive. The reason is that during a search, database draw scores of +/- 1, 3, or 5 get compared to other eval scores, some of which are endgame db scores and some heuristic eval scores. If the PV has a database draw score, it only means that no other variation leads to a better score, but those other variations can have both db scores and heuristic scores. Heuristic scores are of course subject to being inaccurate.
In practical use, you can usually tell when a database draw score has a high probability of being correct, and when you should not trust it. I look at the number of pieces that are on the board, and during the iterative deepening search I look at how many successively deeper searches return a database draw score. If for example there are 20 pieces on the board and after a long search you finally get the result of db draw, this is not a conclusive result. But with 16 or fewer pieces on the board, if you get db draw scores returned at depth N, then N+1, N+2, N+3, N+4, N+5, then this is an indication with high probability of it being a true draw. But it is not a certainty.
+/- 7 scores are used in kingsrow to indicate a draw by repetition. These results have the same uncertainty as database draw scores, and for the same reasons. Also, in some small percentage of cases, repetition draw scores can be incorrectly indicated due to something called the Graph History Interaction problem that affects most game programs using transposition tables.
There is more about this subject in the Kingsrow help file, in the section "Using Kingsrow", "How do I...?", "Know for certain that a position is a win or draw or loss?".