Omega ‘sidewinder’ savonette?

Love this but slightly flummoxed ! 38……. under the dial which would suggest an early 1910 movement but the case is later I believe. Did the jewellers buy old movements and pop them in. Notice no Omega branding on the face either. Great size at 35.5mm and large lugs, 18mm. A slight mystery. What are your thoughts.
Regards
Jon