That doesn't sound credible to me. The twin air engine uses a replaceable paper element type filter. To change it you unscrew the filter housing, remove the old element and sealing O ring. Clean the housing and install a new filter into it and fit a new sealing O ring, then screw the housing assembly back into it's location on the engine. Wrong filter? poppy cock I say! Maybe, if they removed the old sealing ring and forgot to install the new one before reassembling? but that would be almost unbelievably unprofessional.
Edit. If they're this unprofessional I can't help wondering what oil they are filling it with - We all, on here, know how very fussy the twin airs are for exactly the right oil if they are to run well and avoid future damage to the hydraulic valve gear.