Mention of the ninja makes no sense

This guy from the future mentions 'ninjas' ... in 1973.

Not only that, but the other cop responds without missing a beat, saying it wouldn't be ninja style or whatever.

The weirdest thing about this was, _I_ was just thinking about it possibly being a kunoichi or some kind of ninja, so that was a bit startling when they suddenly said that.

However, how would cops in 1973 know about ninja? (Can't say 'ninjas', as 'ninja' is a japanese word, and thus always also a plural)

The ninja boom didn't begin until the eighties, with all kinds of ninja movies, although books about ninja did appear in the west earlier, and the actual ninja existed way before, in the mists of Japan's interesting history.

It's of course plausible, that people would've known about ninja in the seventies in the west, but what I want to know is, HOW can the ninja be so popular in pop culture in 1973 that cops know it as a cultural phenomenon so easily?

Anyone in 1973 that knew about ninja would've had to have read some books or researched japanese history or something like that. It wasn't yet in the 'public consciousness' back then, so even though our guy from 2006 would definitely have known about it, WHAT is that cop in 1973 doing answering a semi-ludicrous statement like that without even pausing to think what our main guy just said?

It makes NO sense that any random UK-living individual, especially a cop, would just respond that way, not only thinking it's a perfectly normal thing to do to mention ninja, but also knowing about 'what style' they would've incorporated (not that the ninja HAD any particular 'style' - whatever got the job done, is what they did, even though they DID specialize and train in specific methods and hone all kinds of skills as well).

This show really keeps shoving modern stuff into supposed 1973.

Of course, therere's the possibility that this is all happening in the protagonist's mind, which would explain all the anachronisms, but they could've been a BIT more accurate anyway (unless it's deliberate).

Maybe it will make sense in the future, but so far, that mention makes no sense.