It can happen pretty quick and in situations you don't expect. So I would not go trashing people to quick.

Responsible animal owner here, I dog went on heat before we had a chance to get her done, she was of unknown age when we got her and in poor condition so desexing was recommend a bit later than right away. Where are in rural area. So no dogs really wandering around. She was either with us, or locked up in her run. She still managed to get pregnant (well she was showing early signs and the vet advised we get her desexed right away). Found out later from friends who are dog breeders, that they can actually DTD through wire fencing. Could have been a phantom pregnancy or one of the farm dogs came for a very long walk.