Did you sneeze or bang your head or anything?
Those can trigger nosbleeds.
My older brother when he was much younger used to have a clot in his nose, and even slight bumps would dislodge it and fresh blood would flow out.
It was a bit distressing, but not a major problem.
You're probably safe. Nosebleeds happen and aren't uncommon.
If you have any other symptoms alongside it, like feeling a cold or flu, then maybe take a trip to your doctor.
And if the nosebleeds keep on coming, or happen to be very heavy, then I'd recommend visiting a doctor as soon as you can.