Unlike with longer distances and temperature, Americans don't strictly use imperial for shorter distances (m, cm, mm). It's on all of the signs and stuff, but we learn metric in school as well as how to convert to and from. In university-level physics classes, they almost solely use metric. So as an American myself, I didn't bat an eye at him using meters. But if they said that it was 30C outside...
It helps that meters and yards are very similar in size. Of course they drift as the distances get larger but in my mind 300m is a pretty reasonable thing to visualize. Just a tad larger than 300yd—about 3 football fields (Inb4 stereotype)
Km though? I still struggle to compare it to a mile. When someone says "50km" my mind has a hard time imperializing it. What's that, like 35 miles?
Maybe memorizing how the km lines up with the mi on my car speedometer would help.
I guess as long as it works it works. I don't have to do much of those conversions though. Here in Norway we are metric in almost all of our measurements. Except for some specialist measures like a carton of eggs is a dozen. We often say things happened a fortnight or so ago, etc.