Yes this happens from time to time, it is just a weird "quirk" of cannabis.
Calyxes can also grow on leaf stems, middle of the leaf like your photos and even randomly on the main stem, well away from any "nodes".
In my diary "cannabis conundrums" and in week 7, I have posted pictures of some weird flower growths that I have found over the years, they seem to pop up every 20-30 plants, so not really common, but far from rare.
Hope this helps,......
Organoman.