1/ This is a really good stretch for the lat and associated musculature and should not be dangerous at all. No stretch should be dangerous for the majority of the population.
2/ If you pull or stain a muscle during a stretch then your either getting way too extreme or your doing it dead wrong.
3/ generally speaking unless there is some kind of serious traumatic event (eg slipping on ice, falling off a roof etc) it’s hard to pull a muscle, as the Golgi Tendon complex will not allow you to strain muscles so much that an individual event will tear it.
4/ most of these seemingly weird muscle pulls are the result of repetitive stress issues that people don’t pay attention too until it catches up with them.
5/ stories of bodybuilders tearing pec and bicep muscles and tendons is usually a negative effect of ped’s. Which causes the muscles to grow in strength faster than the connective tissue can and therefore putting excessive stress on the tendons to the point of it’s failure to be able to deal with the demands of the superiorly strong muscle.
6/ doctors telling you that you have strained a musscle is the first response to any minor muscular complaint. Did she/he also give you some anti inflams and or pain killers and tell you to come back in a week or so if your not feeling better?
7/ stretching for the majority of people should be relaxing and beneficial, not stressful and hurtful, unless you in the hands of an expert therapist and or your looking for extreme rom of your joints.