In British English (outside of the scientific community) turtles and tortoises are very different things.
It was only when I studied tortoises that I learned to accept that tortoises (Testudinidae) are a Family of turtles, and so others calling them turtles is fine. However, you will never catch me calling a tortoise a turtle when the word ‘tortoise’ is always available.
I do like how on iNaturalist the Order Testudines lists both Turtles AND Tortoises, not just Turtles. 
