I have also had the ‘weekly’ challenges show up again after a couple days. I completed the weekly flashpoint in the EDZ on Wednesday and it showed up again on Friday. And what is that reset time? I thought it would be 10 am PST. But I’ve had some instances where I completed challenges early in my playtime (around 6-7pm) only to have them show up again when I looked near the end of my nights (around 12-1am right now since D2F released, I’m not gettting my chores done)

So... I'm not sure how to explain the timing difference (you say Friday, Bingle says Saturday evening), but there actually was an unintended reset of some weekly challenges, apparently:

After further investigation, we have determined that the Gambit, Crucible, and Story Weekly Challenges did reset at 5 PM PDT Saturday instead of at the Weekly Reset. This will impact acquisition of Powerful Rewards. For updates as we investigate a fix, see https://t.co/t6ksP5BMIx https://t.co/BSrLfYcSjz

— Bungie Help (@BungieHelp) September 9, 2018

Not sure if you're misremembering or Bingle is wrong, there does seem to have been a lot of confusion on their end when they were investigating - initial report was that it hadn't happened, LOL. But, in general, it's very possible that you completed a weekly challenge, and then it showed up again at a time when it really shouldn't have. I think it may have even happened to me, although I'm not sure - over that timeframe I had one character who had already had those challenges available, and 2 others who were approaching that point, and it's hard to remember which character did which challenge at what time. Doesn't sound like this weekend reset is expected behavior going forward, though.