That all seems laughably minor stuff.
The nuclear issue is, in my opinion, by no means clear-cut, there are arguments on both sides (not to mention a long history of lies, corruption and creative-accounting associated with that particular industry that makes it even more difficult to work out the truth of the argument).
I don't really know about GMO - not sure what's so terribly wrong with giving consumers information. It seems very naive to assume "it's science, so it's good" when it's also commerce.
I've always rolled my eyes a bit at the hippy alternative-medicine type beliefs associated with certain strands of 'the left' - the middle-class type who shop at Whole Foods (itself owned by a hard-right-winger, no?). But it's a minor side-issue compared to everything else. Those sorts of slighly-cranky traits are almost independent of left-right politics. You find people with them across the whole political spectrum.
That the article concludes with the bizarre suggestion that such faddishness is a specific trait of 'the extreme left' really does the writer's credibility no good at all (not to mention the implication that Sanders is himself 'extreme left' - he really isn't...the _actual_ hard-left regard even Corbyn as a conservative backslider, and Sanders is to the right of Corbyn)
There are more important weaknesses one could find in Sanders, I think, if you wanted to. E.g. he didn't, from what I could see at this distance, strike me as being exactly up-to-speed on racial politics or sensitive to the concerns of African-Americans, and he's just plain old (that being a problem with Corbyn as well). And he has never been subject to the full onslaught of the Republican machine, so has never really been tested. But that article was weak.