That sponsored article should be categorized using their book titles advertised at the bottom: "The Content Marketing Handbook", "Hipster Business Models" and "Everything is Bullshit".
That said, without actually describing in more detail how they measure it, yes, it's very, very circumspect. I'd wager even more so than just asking people "hey, when do you feel most productive?" Because the time I mark something done in JIRA, say, is barely correlated to when I spent the most time and focus on it (and even that correlation is not being picked up here. That is, I'd say "The time I spent the most effort on a problem is within 4 working hours of the time I marked it done, unless I completed it first thing in the morning, as I might wait until the end of the day to mark it done, and also barring a whole flurry of initial effort, it not getting me anywhere, I take a break, realized I was thinking about it wrong, go back and get it done in minutes").