>>104075532This is domestic sales only, so foreigners shouldn't appear. Although, as the sidepanel notes, there is a possibility of having your digital sales count if you VPN to Mora, though I don't know if they keep track of who is buying with a foreign credit card when supplying their data to Oricon. However, if this was the case it probably would stand to reason that others would have a similar bump in sales from foreign fans.
The Nijimale ones usually (always?) come with raffle tickets for Meet & Greets and the like, so fans are incentivized to buy physical. Hololive doesn't do those, but I think some of them had more luxurious merch options when you buy them physical. What with her ranking on Billboard Top 100 artists, it could also be simply a sign of casuals outside the vtuber bubble buying her stuff.