Four Hour Delay

Hello. We were flying Barcelona to Istanbul to Mauritius.We were supposed to have a simple 90 minute layover, but the Istanbul to Mauritius flight has been delayed 4 hours and 15 mins. We are currently sleeping on a bench in the airport with our 18month old, but that's not why I am here. The message I received was the delay is due to force majeure reasons. As far as I am aware, this would mean it's not possible to claim compensation. However, we noticed every other flight is leaving okay and there is no major snow storm in Istanbul or Mauritius so we asked at the help desk why the large delay. She said it's because the aircraft was delayed on a previous flight. This would be an operational reason, right? If so, we could claim via EU261 as we originally departed from Barcelona? Or is EU261 not applicable for this section of the booking. Thanks, a very annoyed and tired Dad.