I think you need to refer to Taxmann's Direct Taxes manual No. 3 for meaning of the word Vocation.
Profession is not defined per se in the Act. It is just said to include Vocation.
Strangely even the word business is not defined per se. In the same section
business includes any trade , commerce or manufacture or any adventure or concern in the nature of trade, commerce or manufacture. For the definition of trade, commerce, adventure and 'nature of trade' you have to refer to the same Taxmann's Direct Taxes manual No. 3.
Both these terms are not independtly defined but both include other definitions. Now when something is not defined, you would have to take an acceptable dictionary meaning.
Therefore you take the dictionary meaning of profession and include the meaning of vocation as per the Taxmann Manual.
You take the dictionary meaning of business and include the definitions of definition of trade, commerce, adventure and 'nature of trade' from Taxmann's Direct Taxes manual No. 3. for the phrase 'business includes any trade , commerce or manufacture or any adventure or concern in the nature of trade, commerce or manufacture.'
For 44AB, if the activity fits into business then business and if not then profession. My view. Please refer to that Taxmann Manual as I am not a professional and do have reason to own one. Now that you have ruined my sleep on this, please let me know what you find out.
If you follow both definitions, even business comes under professions and professions can be business.