In both years, even more dramatic reports of humanoids from the deep were reported in North America, in Indiana in 1955 (when a hand nearly grabbed an unfortunate swimmer in the Ohio River) and in 1972 in Thetis Lake Vancouver (which has largely been written off as a hoax). It has not escaped notice, especially in the Indiana case, that The Creature From the Black Lagoon had been released in theaters the previous year. Humanoid sightings in general were big in both years. In 1955, all sorts of sightings of odd humanoids were centered in the Ohio River valley (see Albert Rosales' 1955 entry in his compilation of humanoid sightings in the context of UFO lore). This was the same year that the infamous Kelly-Hopkinsville "goblin" UFO encounter occurred in Kentucky. No such wave occurred in 1972, but UFO sightings would skyrocket in 1973.
There is no real back story, that I'm aware of, to the Loveland Frog. The 1955 reports have been seen as possibly relating to UFO sightings, similar to the wave of humanoid reports in France in 1954. But no one has tried to stake out a taxonomy for the frog, claim it as part of some larger picture, or even suggest some Innsmouth folk moving out west. But this hasn't stopped the legend from growing into a festival, and a local football club.
I very briefly stopped in Loveland two years ago, in the area where the iconic sighting by Officer Ray Shockey (the second of the officers has since said he only saw an iguana) occurred.
Riverside Avenue, where the sighting took place
The Little Miami River in the area of Shockey's report