Most IPv6 packets are encapsulated in Ethernet frames which use MAC addresses. What may change is the vendor specific MAC address could be replaced with a MAC address generated by a cryptographic hash to preserve privacy.
This is paranoia about all the wrong things, focusing on irrelevant details and ignoring what’s important.
The suggestion is simply this: Don't embed your MAC address into your IPv6 address because it's a unique identifier that can deanonymize you even if you shift networks.