Yes, we have city water, a long 100 foot or so copper pipe running in the opposite direction (west) to where our pole pig is located (east). I don't know what material the big water pipe is made of (probably metal, whatever they used around 1950) but yes, it's likely our neutral current went back to our west neighbor's water pipe ground, up his service's neutral, then travel about 3 pole separations along the POCO ground wires back to our pole pig. Turns out a neighbor to our east feeds off the same pole (it's hard to see, but there's 5 wires running down the pole, 4 hots and one shared neutral that is split lower down the pole), so her neutral and ours are tied together, and both shared the broken connection. So some neutral current may have gone into her water pipe, and to other neighbors water pipes and then to their service neutrals.
Our ground wire inside the house looks to be #10 or #8, whatever the code called for in 1952. Now that the POCO fixed the broken wire, we now have a #2 neutral, as the house did when new.