I had sort of the reverse, working with German-speaking coworkers. I used the term "schpiel" to refer to a long talk I was going to give. This led to a moment of confusion because that's not what the word means in German. It means "game" or "play" and in the context they thought I meant to imply that I was not taking the speech seriously, or maybe wasn't going to be completely honest. Almost like a con. That's probably how the loanword first entered the English language, and its meaning has drifted over time.
Yiddish and German are like Spanish and Portuguese. They are of course different languages, but there is a lot of overlap in vocabulary. I don't know which language was the vector for the word.