We shouldn't limit our use of language based on laws written 100 years ago. It's pretty clear that those laws are inadequate to restrain the monopolies that exist now.
Said another way, you might be right about US antitrust law, but when that law was written the technology didn't exist to create "vendor lock-in" on millions of products at once.
I am curious about the example though, from a legal perspective. Would the only seller of gasoline have a monopoly, even if other fuels were available, and the only barrier to using them was the switching cost of buying a new vehicle?
Edit: For what it's worth, wikipedia uses the word monopoly when "a single vendor controls the market for the method or technology being locked in to".
https://en.wikipedia.org/wiki/Vendor_lock-in
