I too learned that the hard way when dropping a family member off. I naively assumed it wouldn't charge me if I tapped out at the same station 10 minutes later.
https://tfl.gov.uk/fares/how-to-pay-and-where-to-buy-tickets...
And about refunds (typically you'd get an automatic refund for a one-off event)
https://tfl.gov.uk/fares/refunds-and-replacements/touched-in...
I always have high levels of respect for companies with such clarity
Having someone pay just to wave off someone is incredibly customer-hostile. Besides, how many people are even committing fraud like that?