I highly doubt the interim Managing Director would lie, knowingly or not, about such a matter...
The Southern 171s will be part of the EMR fleet by the end of 2022, regardless of what the TOC may or may not have said, as they have very little say in the matter anyway. It is a matter for Porterbrook/Eversholt as they are ultimately their assets, from their point of view it doesn't matter where they run as long as they generate revenue (i.e. a TOC is leasing them), and if they can guarantee use for several years beyond the end of the current GTR franchise then it is a win-win for the ROSCOs.