Rodent on airplane, cancellation. Is airline excempt from paying reimbursement according to EU laws?

Hi, I was booked on French bee flight BF 711, PPT - SFO - ORY, departure Jan 09th 07:15 am, arrival in ORY Jan 10th 3:30 pm.

After 4 hours of delay in the airport of PPT, the flight had been cancelled. After transport to a hotel, I was rebooked onto flight BF 5711 (different flight number), same route PPT - SFO - ORY, departure Jan 09th 11:45 pm, arrival in ORY Jan 11th 08:05 am. This replacement flight flew without issues.

I requested a compensation of 600 € because of a flight cancellation according to EU laws, and sent that to the airline via their online form. They claim they arent responsible, quote from their answer:

However, it is important to point out that Article 14 of Regulation 261/2004 lists various exceptional circumstances exempting the carrier from any liability. Therefore, we inform you that French bee was compelled to delay its flight due to the presence of a rodent on board the aircraft, necessitating a review of safety conditions prior to departure.

In this situation, the responsibility of the company is not implicated.

So my question is: is an airline excempt from paying reimbursement EU laws, if they find a rodent in the plane, claim its a security risk, and thus refer to extraordinary circumstances?

Also, in the response they claim its a delay, when the flight was cancelled, and the replacement flight had a different flight number (BF 711 original, BF 5711 replacement). Do I have a chance of fighting this in court?