Comment on the meaning
This stanza seems, as noticed the experts, is a little out of context. In my “prose explanation,” you could see that I explain this shift by a kind of side-remark on Ódhinn [Ódhinn is another way of spelling Odin - ed] feeling the need of bringing some details on the circumstances of his sprinkling at birth. This assumption supposes that Óðrœrir [a container for the Mead of Poetry - ed] existed before Ódhinn’s birth, i.e. there has been a primitive Óðrœrir or, in order to reconcile all versions of our mythology, that Audhumla’s [a cosmic cow which is representative of sustenance amongst other things - ed] milk is called here Óðrœrir because its magic properties.
Ódhinn’s uncle was in charge of his education and gave him ‘knowledge’, i.e. magic. This confirms the well-known importance of mothers’ brothers in ancient Germanic civilization. These nine songs originate from giants’ knowledge, often qualified as “very knowledgeable” in the Eddas. We will see in stanza 143 that the giant who brought the knowledge of the runes to his people is named Ásviðr (one of the Æsir’s Tree) what obviously refers to Yggdrasill [aka world tree, a symbol common in many mythologies and representative of the totality of existence - ed], and which thus seems a good candidate to name Ódhinn’s uncle.
Stanza 143 is also often said to be disconnected from the others stanzas, which we just shown being false, in our ‘Mystical meaning’ above. This shows us that the major coherence of Rúnatal is observable only through a magical understanding of the poem.
Again in my ‘Prose explanation', I consider this stanza as an announcement of the eighteen songs that Ódhinn will deliver in the last stanzas of the poem: it brings coherence between Rúnatal and Ljódatal.
Commentary on the vocabulary
Bölþorn means Böl-þorn = Bad-thorn.
The verb ausa, here ausinn in the past participle, means ‘to sprinkle’. This verb can be used to indicate prosaic actions, like ‘to cover (dust)’, but it has also a ceremonial tinge. The children were “sprinkled with water” then named by their parents in pagan times. It was a family-only ceremony. We do not know any further detail about it, but it probably was the ceremony by which the child was accepted in the family, and became exposed to the duties and rights of free person. In Roman antiquity, the ceremony of purification by water was done on adults by a magistrate, and was called a lustration. In the Christian culture, that looks much like baptism, it is thus necessary to distinguish this ‘Germanic Heathen sprinkling’ from Roman lustration and of Christian baptism. This why I propose you to simply call it a sprinkling since the sagas say: “the child was sprinkled with water.”
The vessel containing the hydromel of poetry is called Óðrœrir (here spelled Óðrerir). It does Óðroeri in the accusative and the dative, here undoubtedly a dative. This name is made of óðr-hrœrir = ‘intelligence-stirrer’. [Recall that óðr as a substantive means ‘intelligence, spirit’. As an adjective, it means ‘furious’ – in our context, ‘furious’ en ‘clever do not oppose as it does now, because we took the habit to confuse anger and furor.]
nam ek af inum frægja syni
Bölþórs Bestlu föður
ok ek drykk of gat
ins dýra mjaðar
 I took  nine mighty spells
from the famous son
of Bolthorr, the father of Bestla,
and I got a drink
of the precious mead,
poured from Othrerir.