Describing vegans as making major dietary changes because they "saw one video" is a pretty dishonest interpretation. Rigorously sticking to a vegan diet can be fairly difficult, and requires you to be very aware of exactly what you're eating -- including innocuous seeming things like food dyes and white sugar, which can often be made of animal products. To me, that doesn't read as impulsive, but instead disciplined.

Furthermore, while the decision to switch to going vegan could theoretically sometimes be done on impulse, one still has to make the decision every single day. It's not just a decision you make and it's done, it's one you must always choose to continue to make. A vegan has to decide to continue to be vegan every day, likely while under scrutiny of themself and others.