Earlier quoted context omitted.
No they picked a certain time frame and compare to the average temperature of that time frame. Nothing more, nothing less. I think the reference time frame is some 20 year period in the end of 20th century, but not sure if I remember it correctly.
From the site the baseline is very clearly stated: What is the Yearly Average Temperature Anomaly? It is the difference between the average yearly global surface temperature and its pre-industrial baseline. The pre-industrial baseline is calculated as the average temperature from 1850 till 1900. The value for the current year is actually the average for the last 12 months, for example in June we include values since…
So calling any difference to the average an "anomaly" seems misleading to me.
The trend of rising temperature may still be "anomal", but that is not what they are referring to.
Your explanation kind of points out the problem, as you also seem to think a "deviation from the norm" is somehow unusual.
If you look at another example, it should be obvious: take the average temperature throughout one year, then plot the "anomaly" of daily temperatures in that year against the average temperature of the year. Then in summer it would be "anomaly hot" and in winter it would be "anomaly cold". Except it wouldn't actually be anomal to be hotter in summer and colder in winter at all.