This is interesting, but the post is very inaccurate. The first picture is Portrait of a Moor by Jan Mostaert, and there's no indication that it's a portrait of Reasonable Blackman:

https://en.wikipedia.org/wiki/Portrait_of_an_African_Man

The second picture was drawn by a modern person, and isn't even supposed to be Blackman, that's what the artist thinks Edward Swarthye might've looked like:

https://www.historyextra.com/membership/black-faces-of-tudor-england/

All that aside, here's what the book Black Tudors has to say about him:

A surname alone cannot confirm a person’s ethnicity. Although Reasonable’s surname would seem to indicate the colour of his skin, it is in fact an old English surname, derived from the Old English Blaec mann, as are ‘Black’, ‘Blackmore’, ‘Moor/More’ and ‘Morris’. It could also be spelt Blakeman, Blakman, Blackmon or Blackmun. A John Blakman was living in England in 1206 and the name was fairly common until the thirteenth century. By the Tudor period, the name was found in Eynsham, Oxfordshire, Fowey, Cornwall, and Berkhampstead, Hertfordshire. Henry VI had a chaplain named John Blacman, a fellow of Merton College, Oxford. A different John Blackeman was buried at Grey Friars Church, London, in July 1511. A third man of the same name was a benefactor of St John’s Hospital, Coventry. None of these men was African.

‘Blackman’ may have originated in reference to a dark complexion, but by the sixteenth century it cannot be assumed to signify African ethnicity. As William Camden noted in 1586, ‘surnames began to be taken up ... in England about the time of the Conquest, or else a very little before’. Theoretically, a man called More in 1566 could have had a Moorish ancestor from five hundred years before, but it is a rather remote possibility. We cannot even assume that ‘Blackman’, or names like ‘Moor’ or ‘Niger’, were originally assigned to men of African origin. Wilfred Niger was nicknamed Niger or ‘the Black’ in around 1080, after he painted his face with charcoal to go unrecognised amongst his enemies at night. The names could also refer to dark hair (Black), or to someone who came from a place called Moore (in Cheshire), More (in Shropshire), Blackmore (Essex), Blackmoor (Hampshire, Somerset) or Blakemere (Herefordshire), or even to someone who lived on or near a moor. In Scotland, the surnames ‘Muir, Mure, Moor, Moore, More’ referred to ancient ‘residence beside a moor or heath’.

It is only because Reasonable Blackman was also described as ‘blackmor’ and ‘a blackmore’ that we know he was African. ‘Blackamoor’ or its variants was the most popular term Englishmen used to describe Africans, appearing in some 40% of references to individuals in the archives, and in literature from at least 1525.