I have a 2nd broken spoke after 300km on a new bike, is it the wheel or me?
Not enough points to comment, so here is an answer instead, based mostly on my own experience.

I've been using a bike as my main, if not sole, mean of transportation for the last 20 years or so. During that time, my weight changed a lot (from 80 to 130kgs (176 - 286 lbs)).
When I was 80, I nearly never broke a spoke (maybe once per 10 000km), and only after a big impact.  

I began to break spoke significantly more often when I reached 95kgs. But it was very dependent on the bike. On some it never happened, on some other it happend more frequently (once per 3-4000km). On one (very cheap) bike, I even broke 5 spoke in 10 km without any kind of impact on the wheel.  

At 130kg today, with a 400€ bike (Trekk 7.1), I broke spoke even more frequently, like once per 1000-1500km. Always on the rear wheel. I changed all the spokes on my rear wheel to more thick ones (I can't recall previous and current diameter though), and since then and 8000km, I didn't break a spoke once.

I spoke about it to 2 repairmen in a bike shop, both said it was just that my weight was too heavy for the bike.

So, to answer tour question, I think it's both you and the wheel. You just have a wheel with too weak spokes for your weight. It can be because of the base quality of the spokes, or because of a bad set up of the spokes tension though.