Unless you have some information that isn't publicly available, then how are you able to determine it is "likely"? For all we know it is made up press nonsense and isn't at all likely in any way.
Season ticket holders get tickets for both games for FREE...
https://southamptonfc.com/news/2018-06-15/pre-season-home-fixtures-southampton-celta-vigo-borussia-monchengladbach
What makes you think that? I think the video is just acknowledging the kit is already out there, not that it is a fake leak by them.
The video was filmed on Wednesday this week.