Texting that one person once a year

One could've been sent without Wifi/LTE, so it was a text message. If it was a new phone, the old message would not have been recovered.

Much confusion

I can change the colors on mine, isn't that what's going on?

No.
When you don't have wifi, on an APPLE DEVICE, it is sent as a regular text message.
When you do, it is sent under Apple's version of text messages, iMessage.

Oooh, ok. I have android ;)

The colored texts are from the iPhone sender. My texts still go out as blue even when I'm not on wifi. So it could be that the other person did get a different phone as you're seeing the texts from the senders phone.