Sometimes we don't see things that are not uncommon, but suddenly catch our eye. A recent lemon harvest of a trial in the Central Valley turned up lots of fruit with enlarged nipples on the stylar end. These are from a 'Limoneira 8A' rootstock trial. Not all of of the fruit was like this, but all of the rootstocks had these fruit, so it wasn't a rootstock effect.
On asking around it turns out, this happens in other places, for example on Spanish fruit:
And on Australian fruit:
And even in many normal years and orchards there is some of this special fruit
During the 2018 spring bloom there were several heat waves that hit citrus growing areas. Dr. Mary Lu Arpaia, UCR Fruit Specialist, surmises that high temperatures make for elongated fruit and quite likely impact cell division at the stylar end, as well. So the more heat spells during bloom, it's likely that we will see more of this fruit shape. It's still good to eat.