No, that's not obvious, in fact that would be the opposite of what a keyboard's auto-correct should do. Because the whole point of having auto-correct is for the keyboard to correct my mistakes, not learn from them or from the mistakes of other people that also don't know how to spell.

For this reason for example Swype on iOS has been basically unusable for me, because it makes more mistakes than I do. And no matter the implementation, now every time I choose to override the auto-correct decision for a certain word, I always end up pausing because I fear that from then on, the word will be added so some personal dictionary that I don't want. Basically learning from what the individual types is a disservice to the individual.

Also, on iOS custom keywords need explicit permission for accessing the Internet. And on Android I found no mention anywhere that Google's Keyboard sends telemetry to its parent. People just assume that for some reason.