I think the bigger question is what happened to the iPhone demand. It’s immaterial for the Apple bottom line if they sold 21% fewer Macs. However, a 21% drop in iPhone sales is significant. The reality is probably much worse than that. I wouldn’t be surprised if they sold 50% fewer phones if not in the first quarter, then in the second quarter.
Nothing prevents people from holding onto their existing phones for an extra year or two while they are facing salary reductions, furloughs, and likely layoffs.
As for the demand for non-Mac computers vs the demand for Mac computers, if I had four kids all taking distance learning school and I only had one extra Mac at home, I wouldn’t go and buy three more Macs so that my kids could attend school from home. I would buy three Chromebooks for $250 each or three Windows laptops for $300 each. If the school districts take it upon themselves to equip kids with a device suitable for distance learning, 99% of them will buy Chromebooks or Windows laptops and not Macs. Apple has let education down a long time ago. Apple has no distance learning platform, no web conferencing platform, and no affordable computing platform suitable for distance learning. Now contrast this with Google that has Google Classroom, Google Meet (video conferencing), and Chromebooks or contrast it with Microsoft that has Office 365, Microsoft Teams and a plethora of cheap laptops running Windows 10.
The city I live in (one of the major US metro areas) school systems use either the Google platform or the Microsoft platform. Apple has nothing at all to offer the education in this pandemic.