Positions are measured in face value — how much of a bond a fund holds, not what it is worth — between two complete trading days, so a move in price can never be mistaken for a change of position. A fund counts as having moved a company only if the amount it held changed by more than 0.5% of the position it started the week with, and it held that company on both dates. Bonds held on only one of the two dates are reported and counted, but they do not count towards the direction.
The “how unusual” figure compares the number of funds that increased their holding against what these same funds were doing to everything else they own that week. Without that comparison, a week when money flows into bond funds generally would look like an event at every company at once.
The ranking is a placing among the companies measured in the same days, not a probability. The score already discounts the tendency of funds run by the same firm to move together, so a move concentrated in one fund family scores lower than its raw fund count would put it.
These are published fund holdings. They show one kind of holder, not the whole market, and a change between two filings is not a trade we watched happen: it may be money coming into or going out of the fund, an index change, or a decision by the manager. Nothing here is investment advice.