Open drain on Attiny85
The datasheet is correct, always. However the simple issue is a little bit complicated due to the clamping diodes 

Each pin has a clamping diode to vcc. In your case, even if you were to turn off the pin, a circuit will be form from vcc, the led plus its resistor, and the clamping diode to the mcu vcc. The net result is that you cannot shut off the led.

The pin itself obviously will be clamped to a little bit over the mcus bcc, as shown in the datasheet.