Do such flights also trigger the ESTA requirement for VWP people?
No. ESTA is required of people who are traveling to a US port of entry to apply for admission under the visa waiver program. You won't be doing that on this flight.
You will, however, need ESTA at the land border:
CBP Expands ESTA Requirements for Visa Waiver Program Travelers
Release Date Thu, 04/07/2022
WASHINGTON — U.S. Customs and Border Protection (CBP) announced today that all Visa Waiver Program travelers intending to enter the United States by land will now have the same requirements as those traveling by air and sea.
Beginning Oct. 1, 2022, in accordance with an Interim Final Rule (IFR), travelers entering the United States, whether by land, sea, or air will now be required to obtain an approved ESTA authorization. Under this IFR, VWP travelers intending to travel to the United States by land must instead receive a travel authorization prior to application for admission to the United States and continue to pay the $6 I-94W fee provided for in 8 CFR 103.7, unless entering within the 90-day admission period.
The I-94 can be filed for $6 through the CBP One mobile application, which provides a more convenient way for travelers to apply for an I-94 up to seven days prior to arrival, review their past travel history, check their I-94 expiration date and obtain proof of their electronic I-94 from their mobile device. The application can be downloaded for free from the Apple App Store or Google Play. CBP encourages travelers to obtain an approved ESTA by using CBP One or the CBP I-94 website and avoid filling out the Form I-94W at a port of entry.