Does red-line curve denotes better result in a graph?
As far as I know, there is no well-established standard. The only universally recognized guideline is "use colors that are well visible, also when printed on black/white (if it's an article) or displayed on a beamer with bad colors (if it's slides)".

I think the most likely explanation is that the speaker was joking.

Personally, in my talks I like to use what I dubbed the "Star Wars light-saber color coding": the 'good guy' (new algorithm of which we are trying to show the merits) is in blue, the 'bad guy' (leading competing algorithm) is in red, and green and purple are used for additional variants (with green=good-ish and purple=bad-ish). But that is also a joke and not a standard.