If you carefully read both the Buttigieg and Sanders memos, I don't think either campaign is particularly confident that it's going to win Iowa, at least not across all 3 metrics. There is a lot of ambiguity ("at representative precincts") and hedging ("winning the SDE count"). 
The Buttigieg campaign does seem fairly confident that it's going to win state delegate equivalents (SDEs). That's the most confident claim in either memo. And it's credible since the Bernie numbers also show him doing fairly well in SDE's.
Buttigieg has now released a more detailed statement and is claiming to have won 28% of SDE's based on ~75% of the vote. That compares to Sanders's statement claiming 28.6% of SDE's based on ~40% of the vote.
