Yes, I was surprised to learn this as well. The fact is documented in the state context portion of the state historic bridge inventory. The irony is that right next to Maine in New Hampshire one can find a cast iron 1880s bridge, and an 1880s pin-connected lenticular truss, as a couple examples.
That is a stunning statistic! You would think that Maine would have a large collection of pin-connected trusses as it is on the East Coast (ie large population in the mid-late 19th century), and has lots of rivers and coastal inlets.
To clarify the significance of this bridge this is listed as the only remaining pin-connected thru truss highway bridge in the entire state!