That area is Frisia...

The map is accurate, according to Bede and his Historia Ecclesiastica, which indeed says that the Angles, Saxons and Jutes conquered and settled in those areas. The problem is the extent to which Bede's account itself is accurate. The idea of distinct and clearly demarcated English ethnostates in Britannia is one which only seems to appear with Bede himself in the 7th Century and doesn't really necessarily reflect the actual situation on the ground.

The pattern of initial English settlement in Britannia appears to have been largely piecemeal, with scattered groups largely integrating or assimilating into extant Sub-Roman British communities, or settling alongside them in land presumably vacated through plague and population collapse. Susan Oosthuizen (2020, The Emergence of the English) argues that, while individual settlements might have persisted, it's unlikely for there to have been distinct "English" and "British" areas of the country as a whole: the English turn up almost everywhere in varying numbers, and it's largely down to local conditions the extent to which they integrate and assimilate, or forge new identities.

The English who settle in Kent, for example, are identified by Bede as the Jutes, but we see no evidence of this identity in use among those people. Instead, they appear to have assimilated themselves fully into the existing British community, identifying themselves as Cantwaras. It's likely that some of the ethnographic identities proliferated in the late 6th and early 7th centuries as smaller polities rose to local prominence and began to expand territorially: the Anglo-Saxon Chronicle gives a fairly good account of the early military expansion of Wessex throughout Hampshire and Dorset, for example, and as control over newly-conquered areas was consolidated, then it's likely that those areas were considered "West Saxon" regardless of the actual ethnographic origins of their populations, whether English or British. A counterpoint to this can be seen in Mercia. Mercia was identified as an Anglian polity by Bede, and Welsh sources such as the Annales Cambriae do differentiate between the Saxonum of Wessex and the Anglii of Mercia, but the Mercians themselves don't really use the term themselves. They steadfastly simply identified as Merciorum. Given Mercia's political nature as a sort of tribal hegemony rather than a more centralised dynastic kingdom, more localised, "tribal" or clan identities remained prominent in Mercia, such as the Hwicce or Magonsaete, which may go some way to explain why a pan-ethnic identity never really took hold there.