"This seems very strange to me as a training pilot"
I very sincerely hope that you meant "pilot under training" and that you are not some sort of instructor!! What was experienced was nothing unusual at all, as has been explained already. If you want to find out about vortex wake, stand near a runway threshold when a 757, or similar, is landing. First time I heard it I couldn't believe it - like a whip crack as it hits the ground. Certainly ensured that my application of vortex separation thereafter was generous.