The "human body measurement" test in that article seems flawed. When you launch the Thermometer app, there's only two buttons: Object temperature and Body temperature.
So I'm not sure why the author tried to measure body temperature by using "Object temperature" mode with "default" setting and measuring the temperature under the tongue. The Body Temperature test has always been accurate for me and matches my higher end forehead thermometer.
Looks like the body temperature update came out a couple months after that article was written, so I guess it works better now. Very cool, I would love to have that on a phone.
Could be the article is written by someone outside the US. If you aren't in the US (I gather—at least in the UK I can speak to personally), the app just doesn't offer body temperature at all because they haven't bothered to get it certified for medical use.
(You can work around this by spoofing your location, but it's not obvious to do.)
So I'm not sure why the author tried to measure body temperature by using "Object temperature" mode with "default" setting and measuring the temperature under the tongue. The Body Temperature test has always been accurate for me and matches my higher end forehead thermometer.