I just opened up my margined account on Interactive Brokers and it shows a large negative cash balance (exactly equal to what I borrowed on margin). I guess an inexperienced trader could've mistaken the negative cash balance as having negative equity value. Alex Kearns had a negative cash of -730k but a positive equity of $16k . Why did Robinhood send him an email asking for $170k in a few days?

Then later after his death, he received another email from Robinhood:

"Great news! We're reaching out to confirm that you've met your margin call and we've lifted your trade restrictions."

Did Robinhood's margin call system make a mistake?