I liked this story because it brings up a few interesting things.
First, clear and proper communication as a scientist is absolutely crucial. Obviously in this case the guy's just an asshole, but the point is that you really shouldn't say anything that may be construed as your professional opinion unless you can back it up. I don't know about everyone else, but this was ingrained in my education and other training. I've made gaffes, but in settings where it doesn't matter much (that's an important part of undergraduate and graduate education in any field) - you'd think someone in this guy's position would have learned his lesson by now.
But second - is a thought like this, flawed as it obviously is, completely invalid and not worth looking into? I'd argue no. Lots of anecdotal evidence suggests there may be some truth in what he said - though obviously it isn't such an absolute. And more likely it'll be far more nuanced - lack of discipline in one part of your life doesn't necessarily imply lack of discipline in another. In fact anecdotal evidence also suggests that this is the case - hence the absent-minded professor, disheveled grad student, etc. stereotypes. You'd have to do real studies to see if there's anything there, but now it's less likely that will happen.
It didn't have to be that way - this guy could have done such a study and kept his personal opinion to himself. Another reason why proper communication is important, but also a segue into the next interesting thing about this - the boundary between casual and professional communication online. Scientists tend not to talk about things the way everyone else does, to the point of sounding crass - political correctness and being gentle with your words can be a professional hindrance. Those discussions traditionally are not visible to the public - they take place in private offices and conference rooms and wherever. But now they take place on the internet where everyone can see.
I'm not suggesting that this person thought that only other evolutionary psychologists were going to see his tweet. He surely knew who his followers were and the wording of the tweet suggests he meant it as a general statement. As I said, he's just an asshole.