I'll echo my comment from the original article and say its definitely a throttling issue with the smaller heatsink. The processor just cannot run at as high-a-clock speed because of the dangers of overheating.

This will be a conscious design choice on Apple's part because they will have the usage statistics from millions of M1 Air users and come to the conclusion most of them will never notice. I don't think its any attempt to 'gimp' cheaper models to upsell the more expensive because the pricier ones still have the same processor and heat sink.

At the top-end there have been noticeable performance differences between the single-fan and double-fan models of the M1 iMac which strongly implies this is an issue, its just only an issue to 0.001% of users.