This morning I randomly had 1000 satoshis in my account and I have no idea why I got them.
The 1000 satoshi is the bonus freebitco gives to the users who become active after a long time of inactivity.
You have probably received an email regarding the bonus.
Read the post below made by TheQuin.
Check your emails. If your account was inactive for a while we will have sent you a "We miss you..." offering you 1000 sats after you come back and complete 10 free rolls.