Is Bill Nye actually a science guy?

He's a man and an idiomatic term for men is 'guy'. He does science. So, I think we can say he's a science guy.

He explained science on a kid's show.  His degree is in engineering, which is applied science. 

If he does science guy stuff.  This is not quite the same as a scientist.  Scientists hold to a more rigid set of criteria than simple "science guy" behavior.  Kind of like the difference between sports guy on the local news and an actual professional athlete.  Sports guy might know a lot about sports, but he still is only a sports guy, not an athlete.  He could be an athlete, but being sports guy doesn't make it happen.

After attending the private Sidwell Friends School, Nye enrolled at Cornell University, where he studied mechanical engineering earning his Bachelor of Science degree. Then he went to work for Boeing in Seattle for many years. However, that doesn't make him a scientist in the full sense of the word. 

So, short answer: not a scientist, just a "science guy" for TV. 

Yup. A degree from Cornell, too, which is hard to get into.

yes. He is ......Original gangster science guy