A problem which releases fumes into the cabin IS a tech fault - no lie there.
The fire service turnout is standard for any urgent return - they spend all day at the airport, and the practise is good training under real conditions.
The O2 cylinder and mask is also a standard first aid response, and the cabin crew training would have prompted it - although it probably wasn't used as the pilot masks can provide fume protection and 100% O2, which a cylinder cannot.
As the flight concluded safely, then it shows the pilots acted in good time to make a safe return before either of them were affected to an extent which would have jeopardised the aircraft - that sounds like a good result to me.