Welcome here on HCM.
Yah it may be due to sinus infection
To stop bleeding do the following.
Make him sit and slightly inclined forward and press soft part of nose with thumb and index finger for 5 minutes.
If bleeding still there than you can do to ice sponging of nose and sinus.
You can repeat these for some time.
If even than bleeding does not stop or it is profuse, than immediately rush to emergency.