I've had people tell me that a kid building things with LEGO bricks is an engineer, so that means Musk is an engineer, too. Apologists will stretch the definition of an engineer in order to claim that Musk is an engineer, as well. It's often stretched so thin that pretty much anyone who built anything would be qualified as an engineer using the definition that also qualifies Musk as one, too.
Many engineers have degrees in physics. It's a perfectly legitimate degree to have for an engineering position. There is no stretch of the definition whatsoever.
A person whose title is 'RF Communication Systems Engineer' and has a physics degree is an engineer.
A person whose title is 'Chief Engineer' and has a physics degree is also an engineer aka Elon therefore he is an engineer.
This is ridiculous debate given Elon leads thousands of engineers daily and given his success there's no doubt that he is making good engineering decisions daily because he is a good engineer.
Software engineers aren't actually engineers because they have degrees in computer science. Especially the kids who don't go to college and start their own companies giving themselves software engineering titles. Giving yourself the title automatically disqualifies you from being an engineer no matter all the things you accomplish.
Given there is no official definition and the definition is subjective, you pretty much can't win this argument.