I'll bet your dad used motor in his car or other engines.
For the purposes of 'understanding' what anticoagulants do (and why 'thinner' blood is better for people with mechanical valves than 'thick' blood), this model works.
The reason warfarin is referred to as a 'blood thinner' is because this is what early researchers thought was actually happening. And it's a description that sticks.
What irks me is when professionals, who should know better, address other professionals who should also know better, with this term (although, to ease my compulsive mind, it's likely that the all know it's inaccurate, but they all know what's actually going on, and it's a term that is very commonly used and accepted).
(Slightly off subject - many trade names are used as generics - Kleenex now refers to all 'facial tissues', Tampox refers to all Tampons, Xerox is a photocopy of any kind, and there are probably thousands of other words that were once trademarks (even if they don't end with X) that have become a generic name for what was once a trademarked product. (And Coumadin also belongs on this list))