On the other hand, were your fish from the same shop? If your fish were from different tanks in the shop, did they use the same net for several tanks?

At any time since you discovered that one tank with Camallanus, would you have used a net or siphon in that tank and then in another? (A seasonal trick - I toss used siphons, and nets out on the air conditioner shell to freeze in the weather. It was two weeks before I could get a net off it. ;) Buckets just go out on the sidewalk.)

Would you have poured water into another tank after having taken water out of the infected tank? Might you or somebody else have had a hand in the infected tank (perhaps to pick up a dead fish) and then put it in another tank or fed fish food without scrubbing down? (I've even scrubbed down with baking soda and dabbed hydrogen peroxide on a couple of items.)

If nothing has been used in that infected tank and then elsewhere and no gravel, plants or filters were moved from the Camallanus tank to the others, you are right, it is probably fine.

I don't mean to sound super righteous about cleanliness. One of the reasons I am touchy about that goes back to my dumb stunts like when I had a tank with 30 + great looking Nothobranchius guentheri in it. They got velvet. In the process of cleaning that tank (the water change prior to the adding of salt and acriflavin) I slopped a tiny bit of water into another tank with another 30+ terrific little guentheri. Two days later I had the privilege of treating that second tank for velvet. (The good news, most of them survived.)