rand() produces numbers above set range in recursive function

My understanding is that this produces a random number between 10 and offset:

random = (rand() % 10) + offset;

offset gets incremented by 1 but never goes above 10, yet when I run this code the variable random gets set to numbers > 10.

code in question:

#include "pch.h"
#include <cstdlib>
#include <Windows.h>
#include <iostream>
using namespace std;

void gen(int offset)
{
    int random;

    if (offset != 10)
    {
        random = (rand() % 10) + offset;
        cout << "random should be between: " << 10 << " and " << offset << endl;
        cout << "random: " << random << endl << endl;
        Sleep(500);
        gen(++offset);
    }
}

int main()
{
    srand(373);

    gen(1);
    cin.get();
}

and the output:

random should be between: 10 and 1

random: 7

random should be between: 10 and 2

random: 11

random should be between: 10 and 3

random: 3

random should be between: 10 and 4

random: 13

random should be between: 10 and 5

random: 10

random should be between: 10 and 6

random: 13

random should be between: 10 and 7

random: 16

random should be between: 10 and 8

random: 14

random should be between: 10 and 9

random: 18