I think you have to look at not just the word reactive but also the context of the sentence in the rule book
" newer technologies such as EFI, or electronic reactive ignitions are not in keeping with the spirit of vintage rules and are not allowed."
so it says "electronic reactive ignitions"
When I asked Matt Shuss he said
Tom can correct me if I'm wrong, but it is to disallow ignitions which adjust to boost, A/F readings, knock sensors, etc.
Which was what I thought it meant
G