That maybe what they mean but it isn't what they said.
The season ticket page which is still there and the one I used to decide to pay up again continues to say the following - it actually starts on the day it is confirmed as being a closed stadium - goodness knows when that date is - arguably every match is behind closed doors and confirmed as such for the forceable future - but it isn't from match day...
Here it is...
"Chief among these is that the club will guarantee a pro-rata refund for any fixture played without fans. This will be automatically refunded to the method of payment used to purchase within 14 days of confirmation, with turnaround time an operational benefit of our new ticketing platform. "
Link to current live page:
https://www.southamptonfc.com/news/2020-06-18/southampton-football-club-202021-season-ticket-information