Exercising after eating is safe. The other answers here are based on personal opinions.
When you eat, the process of digestion is aided by the parasympathetic nervous system (rest and digest). When you exercise your sympathetic nervous system releases adrenaline, which inhibits the peristaltis in your gut. This in terms makes the food move more slowly through your intestines and causes indigestion. Some of the effects of this are heartburn, bloating and diarrhea. However, this is very individual, as it depends on the ratio of activation of your sympathetic versus your parasympathetic nervous system when exercising. Some people can eat right before and not feel anything, while others need at least 2h before practice. Just doing pull ups will not get your adrenaline pumping as much as doing whole body training such as sprinting or doing contact sports.
Try doing pull ups after your meal and see how you feel. Purely medically there are no dangers of doing pull ups after eating.