You're assuming that smoking was the cause of the change, not an effect. For some, I'm sure it was a cause. I don't think pot, or any drugs should be taken lightly. It's just that anecdotal evidence is, inherently, completely useless.
A good friend of mine smoked a lot of pot and drank quite a bit his first year at RIT. RIT isn't an easy school. Yet he managed to maintain above a 3.5 GPA and a part time job. He actually got second year status before I did. And the funny thing about that, is that I'm a year older than him. He got there first because I fell behind my first year. That first year, I didn't touch a single substance. My second year, which was probably the best year of my life, I drank quite a bit. I think you see where I'm going with this. These stories are anecdotal, but they contradict other anecdotal evidence. Neither provide any answers.
But at least that site doesn't have outright false information on it, only suggestive phrases and weasel words. They aren't like those nutjobs that claim pot causes every ailment known to mankind.
Bassoon, n. A brazen instrument into which a fool blows out his brains.