The fact that the decrease was so much larger than the proportion of gun-owners who attended might suggest that NRA conference attendees aren’t representative of gun owners as a whole, and are more likely to cause injuries. Of course, there are multiple possible explanations for why this might be so: It’s possible that NRA members are less well-trained, for instance, or it’s also possible that they just use their guns more often.
Even if you brought your gun with you to the convention city, there are probably many other attendees for whom that was too much of a hassle (for instance, because they were traveling by air instead of in their own vehicle). And it’s quite possible that your weekend routine would ordinarily involve going down to the range, or varmint-hunting, or some other shooting activity, that you would have foregone in favor of going to the convention instead.
In any event, the result here is just that there is some effect, without saying why there’s such an effect. Cases like yours might be instructive in determining that why, but they don’t negate the fact that the effect exists, and so are beyond the scope of this paper.