Yes, that is a baby seed.
It must have come from somewhere, so be very thorough in looking for either male flowers or male stamens, they can be very tricky to find, so close inspection is a must. Occasionally "phantom" seeds can appear, but in 99.99999% of cases, it is due to male pollen, not phantom pregnancy.
For pictures of male flowers and individual male stamens (bananas), go to my diary "cannabis conundrums" and in week 7 you will find them, as well as many other pictures of weird and wonderful things cannabis plants are capable of.
Hope this helps,..........
Organoman.