Yes, it is interesting, and having an obese mom during pregnancy might be one of the many triggers of autism (there are likely several different reasons).
However, I am sure we all know super healthy, type A, spends-their-entire-life-in-spandex-showing-off-that-booty (and going to or coming from yoga and or pilates) yuppie moms with kids with autism or along that spectrum. So clearly obesity is not the only, or even close to being the main, cause of autism. Furthermore, they recently identified several genes related to autism. I also believe paternal age is somewhat related.
Obesity could be a marker for other underlying reasons. Obese moms might also share several other characteristics: being poorer which could lead to lack of medical care, lacking in certain nutrients in their diet, drinking while pregnant, being sedentary, etc, etc Obesity, per se, might not be the reason.