Still, I think it was bad advice to suggest a larger displacement bike to a beginner.
And I would have to disagree, I am a beginner and I have a 500, in fact my MSF class was taught using the Harley Davidson Street 500, which is also a 500cc bike with a curb weight of 514 lbs (100 lbs MORE than the Rebel 500 ABS). The Rebel 500 ABS weighs 414 lbs curb weight and really isn't that much more than the 300.
The 500 is a great beginner bike as its not geared for racing and starts are nice and easy and smooth. Really the only different between the 300 and 500 is that the 500 has a bit more to give at highway speeds and the 300 doesn't. The max difference between a 300 without ABS and a 500 with ABS is 50 lbs.
2018 Honda Rebel 300 curb weight - 364 lbs
2018 Honda Rebel 300 ABS curb weight - 370 lbs
2018 Honda Rebel 500 curb weight - 408 lbs
2018 Honda Rebel 500 ABS curb weight - 414 lbs
So with this information, why would you say that the 500 is not a beginners bike? And lets not talk about price because even at $6400 a new 500 ABS is still totally in the average beginners price range (for newer bikes)