Air carrier Captain reported a ground conflict critical during taxi. The Captain took evasive action to avoid a collision.

Narrative

After landing ZZZ Runway XXL; taxi instructions were Taxi 1; 2; hold short of 3" awaiting gate to open. After turning onto 2; I observed strobe lights ahead and to the left; but could not identify their origin and could not understand why a taxiway leading to the cargo ramp had strobes flashing. A B-757 was in front of us on [taxiway] 2. As we approached the 757; I noticed a small; single white light well below the flight deck height. Fortunately; I realized in time it was the position light of a high-wing GA aircraft (possibly C-172?). I applied brakes and stopped within feet of the preceding aircraft. I turned the landing lights on to see better and at that point; the red anti-collision beacon at the top of the tail came on and made the aircraft much more visible. I suspect the pilot ahead turned the anti-collision beacon off and left the strobes on in error after landing. The First Officer (FO) and I saw the aircraft at the same time and were surprised how dark the aircraft was without its anti-collision beacon operating."