Well, according to the article 3/5 of foreign buyers paid cash, 1/3 of domestic buyers paid cash, and 1/5 of all buyers are foreign cash-only buyers.
1/5 (all buyers) = 3/5 (foreign buyers)
So one in three buyers is foreign. Which means two in three buyers are domestic, which means two in nine buyers is a domestic buyer who pays cash. So that puts the number of cash-only domestic buyers higher than foreign investors. That means that it's roughly the same absolute number of domestic cash-only and foreign cash-only (allowing some fuzziness in the numbers), not quite mostly foreign cash-only.
We can safely then conclude that the article linked does not support the claim that the people bidding cash are mostly foreign.
Buying != Bidding. You don't just bid on one property and buy it.
When you're in an auction market, which has a segment of bidders that are more accustomed to bidding over with cash, you're going to see them push auctions into the cash over range more frequently, even if they aren't the ones ultimately buying.
A reasonable hypothesis. Since there is no evidence that domestic cash-only and foreign cash-only buyers have different bidding patterns, we can then conclude (contingent on your latest hypothesis) that the link with the stats does not support the idea that it's mostly foreign buyers bidding up the price.
It's not a hypothesis - it's part of auction theory for markets that use absolute and reserve auctions. Why are you so adamant in attempting to redefine this to dismiss it?
1/5 (all buyers) = 3/5 (foreign buyers)
So one in three buyers is foreign. Which means two in three buyers are domestic, which means two in nine buyers is a domestic buyer who pays cash. So that puts the number of cash-only domestic buyers higher than foreign investors. That means that it's roughly the same absolute number of domestic cash-only and foreign cash-only (allowing some fuzziness in the numbers), not quite mostly foreign cash-only.
We can safely then conclude that the article linked does not support the claim that the people bidding cash are mostly foreign.