I agreed with you at first, but I recall the Bay Area having one of the earliest shutdowns in the US, and that started March 17. While some companies were definitely sounding the WFH alarm about a week prior to that, I think the March -> April jump would've been more incongruent with April -> May jump unless COVID wasn't the only driving factor behind the August -> March growth in the first place.
Anecdotally, I saw a lot more people ordering online in the last two weeks in March than in late April and on. (And, based on the empty shelves then, probably an equivalent increase in in-person stocking up, too.) Remember that stores were running out of stuff before official shutdowns happened, too.
I'm curious what week by week data would look like.