You should download the ATmega328p datasheet and study the parts about the Timer/Counter Control Registers you are using: TCCR2A and TCCR2B. The bits you set are to control the "Compare Output Mode" (COM) for OC2B and the "Clock Select" (CS) for Timer2. You don't set any Waveform Generation Mode (WGM) bits so the chosen mode is 0: "Normal". In that mode, the timer counts from 0 to 255 and repeats. Setting COM2B0 causes the OC2B pin to toggle each time the count passes the value in OCR2B. The ISR moves the value forward by 100 each time the compare match causes an interrupt so the effect is a square wave that toggles every 50 microseconds (100 microsecond period = 10 kHz frequency).
For 70 microseconds ON and 30 Microseconds OFF I would use a Fast PWM mode with TOP set to 199 and OCR2B set to 139. Then there is no need for an ISR.