Am I right in thinking that this construction of the past tense with gwneudd (I hope I have remembered that verb correctly) is a virtually exact parallel to the archaic English construction with 'did' (e.g. 'I did see' as an alternative for 'I saw')?
Yes, and 'gwneud' is used very extensively in spoken Welsh, in particular in the North to form the past and future tenses.
It sounds like it, but it's an artefact of the text to speech which while being good is not perfect
That's present perfect -- which in Welsh would be Dw i wedi ffonio Ceri Lingo.
Two things. 1. Since this is not a negative statement or a question, why is the g dropped? Also, what do the numbers mean before each persons comment?