Chris, Well, on this one, it will be mostly speculation. We know so little about why these plants do the things they do, because there has not been a lot of scientific research into the biology of them.
I have seen a number of types of sempervivum do this. A rosette, for some reason, starts to grow tall, but does not form the bloom crown. In every case I have seen so far, the rosette involved bloomed in the next growing season. What I think is going on here is that the plant has matured enough to start the blooming process, but other cues in the environment are inhibiting the flowering because the growing season would not be long enough to allow the flowers to form and seed to mature.
So I think you were correct in suspecting blooming, but its just been delayed a bit. Please make of note of this plant's location and let us know if it blooms next spring.
I had a number of S. 'Green Gable' in a trade a couple of years back that arrive and all were tall. I thought, at that point, that this was a unique feature of that variety. ((gables on roofs, you know!)). Of course, they all went on to bloom without making chicks, so I lost that variety from my collection before it even got started. I have some S. 'Fuzzy Wuzzy' from a spring trade this year that are also tall. I'm watching them closely, hoping to get some offsets, before they bloom as well.
