I agree with you. However, I doubt that whoever made this model was really thinking anything about scale. I'm assuming the ship is about the same size as the BoBW kitbashes...maybe even the same size as a standard Miranda.
Oh they 100% were not thinking about scale. They rarely ever do.
But... just logically, a window will generally be more universal in size than any other component. Warp nacelles have no defined size that they must be, whereas windows should generally have a much less dramatic difference in size. We can't be EXACT... some windows are larger than others, but it's unlikely that a window would be like, 20 meters tall. On the flip, there really isn't any reason a warp nacelle could be in the style of a Galaxy-Class nacelle but have wildly different measurements.
I'm not one to try to do any sort of calculations based on sizes or anything, I rely much more on the good 'ol eyeball method. Going by windows, the Trieste is MUCH smaller than a Galaxy-Class.
Comparing directly, the Trieste is just...
weird in the placement of it's windows, which would seem to be closer to "skylights" than windows on a wall. That being said though, looking at just the windows... I actually think the Trieste appears to be
smaller than a Miranda. The Miranda seems to have two decks on the "edge" of the saucer, while (not really visible in this picture), Trieste only appears to be a single deck (judging by the windows, one deck that if there were windows on the side walls, would go floor-to-ceiling).
I think the "back end" similarities to a Miranda at that point are more circumstantial... the ship has a somewhat similar build style to a Miranda, but whereas a Miranda has at least 4 decks in the raised section to the back, Trieste has like 2 max.
I really think going by the windows, the Trieste's saucer is a single deck, with the windows positioned on the ceiling. It might eek out a second deck as the saucer slopes up towards the middle.
I think it's a fairly tiny ship.