Paypal giving me free money

[malibustacy]

So, I usually pay for my games or steam wallet top ups using a credit card, ..the credit card I was using expired so I started using the funds in my Paypal account.
I made a few purchases, nothing too expensive and figured soon one of these transactions would be rejected as I knew I was near the end of my Paypal funds, after about $30, I realised that steam was accepting all transactions, and when I checked my paypal, the transactions were recognised, processed and accepted, well after reaching a balance of $0 ...what's happening here? anyone had the same?

[Joko]

maybe because of https://www.paypal.com/webapps/mpp/billmelater-productoverview
https://www.paypal-promo.com/billmelater101/index.html
just like credit card, paypal will bill you later to pay for your purchases

[HLCinSC]

You can also set Paypal to auto withdrawl from your CC or bank account when a purchase exceeds your Paypal balance.

[malibustacy]

I've set up a link to my credit card before (the one that expired) but never to a bank account, ..I've also never set up that 'bill me later' thing