That's a "What the [anything I write will be auto-censored, so use your imagination]?!" moment with a vet, and a reason to yell at him.
However, a topical application is much safer than an injection. It sounds like it was probably topical. And I have no idea why they would mix the two medications -- one alone should be enough. Either they used both, and charged you for unnecessary medication, or they used one and double-charged you for both, or... something weird was going on. That's not normal.
You're in Vancouver -- which vet did you go to? I've had to fight hard with Westview in North Vancouver before about using just Revolution. I had good luck going to West Arbutus in Kits, but we went for mysterious-woes, not mites, so I don't know what their attitude towards it is.
Did they give you the rest of the Revolution vial so you can do the remaining treatments yourself?