That wouldn't make you a billionaire or anything, but it would make you someone who primarily relies on capital rather than labor for income. Your economic interests would align much closer to a billionaire than to someone who lives paycheck to paycheck.
[1] https://www.kauffman.org/reports/the-anatomy-of-an-entrepren...
I can easily melt ice into water, but for most solids, that's very hard for me to do. It still makes sense for me to categorize ice as a solid though, rather than saying that there's no reason to categorize it separately from other liquids.
Their original complaint wasn't about defining these groups (one can debate that classes are supposed to be more rigid than this), but the "collapse of all indenties" into these two buckets - which material dialectics calls for. It's a criticism specific towards Marxism and its notion of "no war but class war".