Part of Buttigieg's "Iowa or bust" strategy (the same approach which didn’t pay off for Bullock) is spending a ton of money there, especially on TV ads and staff. So the idea that this Iowa poll, in which he’s barely doing better than Biden and not even leading Trump, "proves" that he’s the most electable candidate is... of course... ridiculous.
Buttigieg is practically unknown nationally.
That will change if he wins Iowa caucuses.
The only relevant GE polls that we currently have are the polls from IA and NH where the voters are paying attention.