I think I know of someone who will want to hear from you. He runs the site at:
http://www.otocinclus.com
He keeps track of all the otos born in captivity and you certainly have proof that your otos have spawned but he will want to see those pictures. He would be able to give you information on how to have the spawn happen again if you want it to and he is going to want to know what the conditions were in your tank like pH and
nitrate and other readings if you have them. I have contacted him before and he is very nice to talk to.
This is a very rare occurence and you can be proud that it happened in your tank. It is so rare that I do not know but one other time on this forum since I have been here that otos spawned in a tank and lived. I had some that spawned one time and my
betta ate them before I knew what to do and even much about what they were. They were no where near the size of your little guy.
I do know that otos do hide out and you may yet find that there are more of them hiding in the plant so be gentle in the cleaning of it with the syphon. You will need to do more frequent water changes while they are tiny though to keep them healthy. If they have any
nitrite spikes in the water it can cause them to be deformed.
Rose