Same with Dragon not saying shit to Robin... unless maybe they never met, Robin only spent time with sabo/Koala/Hack, just like Sanji with Ivankov, doesn't mean they had to meet Dragon.
Sanji and Ivankov barely speaking makes sense
Sanjiβs training was fighting the 99 masters of Okama Kenpo for the recipes
As far as we know Sanji barely spoke to Ivankov
Like you said an argument could be made for Robin and Dragon as well
Better mastery over her fruit power + basic Fishman Karate
Those are things sheβd learn from other Revolutionary members
We donβt know how much Robin and Dragon actually interacted