If the gyro is not corrected for Earth rate, then the path followed will be irregular. It will depend on latitude, speed and direction travelled. This however is not within the scope of the ATPL nav syllabus, so don't panic! If you had heard this as feedback, then someone has their feedback confused.
If you still want an explanation :
A gyro that is not corrected for Earth rate develops an error at a rate depending on latitude (and therefore the direction and distance you have travelled). Direction actually tracked depends on the error, and that error is changing on a daily cycle (actually a 23-hour-56-minute cycle!). Therefore the error at a given point on a track depends on how long you took to get there, and so on your speed. This is of course all compounded by transport drift, and is beyond any but a fairly competent mathematician (rather beyond me!) and certainly beyond the retired RAF navigators who write the learning objectives and most of the questions
!
If you have any further questions feel free to email me - I was nav instructor at SFT until their fall.