Oh, that's not all that unusual, Julia. Sometimes a single lily will decide by instinct to take a years vacation because it senses it doesn't have enough stored resources to support a full stem and flowerhead--and needs an extra season to rebuild. Next year it will have a slight advantage over its partners and put on a real good show.
Another cause (when you see something like this) is a small bird that lands and takes off again whiile in persuit of a moth or something; and all though it not immediately apparent, they may damage it just enough to cause that condition. I have a Chickadee with a nest just outside my lily garden and this spring she developed a bad habit of perching on the same two lilies before she jumped to the nest to feed her babies. I pounded in a couple of tarp poles for her and problem over but the damage became apparent in a couple weeks--no flowers this year. Even a bunny or cat brushing over young tender tops can do enough damage to the cell structure at the young tender top and can cause something that looks like what you have. But not to worry.
It wasn't chewed off, just never developed any buds or so it seems.
