Nagato awoke the Rinnegan at seeing His Parent kill, thats a Manga fact so stop your useless lies.
The only fact here, Nagato had the Rinnegan and used it when he saw his parents killed.
Fact it takes an emotional event for Uchiha's to awaken a new power in them Madara implanted His Eye on Nagato both as He said to Jiraiya His power did not awaken till He saw His Parents kill in front of Him. Manga Fact don't argue it's their in Black and White for all to see.
The fact here, "the power did not awaken", does not mean that his eyes were not already rinnegan.
nope!madara give nagato 2 sharingan as a gift to test uzumaki DNA.and cause of that uzumaki DNA nagato sharingan became rinnegin!
When eyes are implanted in the Narutoverse, their powers can not be turned off. Nagato always had his Rinnegan activated in the Manga = implanted. If Madara implanted his Sharingan eyes in Nagato then he would have a sharingan, or even if Nagato's Uzamaki DNA was the catalyst for the Rinnegan, then he would have been able to at least switch back and forth from Sharingan and Rinnegan, but he couldn't.
When Madara was EMS'd he revealed that he unlocked the Rinnegan prior to his death. Clearly with enough time to have them implanted in Nagato. Kabuto modified Madara by bringing back his young body with all the powers he had acquired up to his death, rather than bringing him back as he was at the time of his death like all the other EMS zombies. Madara was able to transition between normal eyes to sharingan to Rinnegan, showing that he was the original weilder of the Rinnegan.
It took an emotional event for Nagato to lose control and utilize the rinnegan. It was already implanted in him and was therefore active, but he was too young to be able to use it. It would stand to reason that his parents and himself thought his eyes were an abnormality, because they were not ninja and would not know what a rinnegan was, additionally he probably didn't demonstrate any unusual powers with them before that incident. Its the same with Naruto in his younger years, he didn't know he has Kurama sealed inside him and he could not utilize that chakra on his own. But under duress, it naturally came out because he lost control over himself.