Sleeping more than 8 hours and oversleeping aren't the same things.
For example, sleeping 9 hours is fine if you have high physical and mental activity during the day.
Sleeping 9+ hours is probably too much if you need such amount of sleep EVERY day, but if you do it once in a while to "compensate" sleep deprivation from previous days, then it's not a big deal.
Quote from the article you posted:
"Of course, not everyone who oversleeps has a sleep disorder. Other possible causes of oversleeping include the use of certain substances, such as alcohol and some prescription medications. Other medical conditions, including depression, can cause people to oversleep. And then there are people who simply want to sleep a lot."
"The “right” amount of sleep proves somewhat individual as some people will feel great on seven hours and others may need a little longer. However, in most studies and for most experts, over nine hours is considered an excessive or long amount of sleep for adults."
Keyword: "over nine". So there is nothing that contradicts what I said above.
Last article looks like clickbait because it has "sleeping more than 8 hours" in the title but in the article itself they talk about "average sleep duration of 10 hours".