The A10 came out in 2016... Facetime came out in 2010 on the iPhone 4, a device running iOS 4 on a an Apple A4 CPU and 2.4GHz-only 802.11n. Surely the A10 can handle making a call.
I'm not sure the the A10, say nothing of the A4, could reliably handle group calls. To be fair to the A4 and A10, group calls weren't a feature of FaceTime until 2018. Could the A4 handle an audio or low-res video call? Probably.
You have a great recall of the timeline. I thought that it came out much earlier but I was mistakenly thinking of iChat AV. "In June 2003, Apple announced iChat AV . . ." [1]