pseudo=yes marks that a house number may not really exist, but has been tagged anyway usually on a corner with the last number of the block. It's hence an indication that the data is pretty correct but not completely. It's a way for saving time by only marking what the number could be if it would have been on the corner. addr:housenumber=* is not the real position, but rather an estimate of the whole blocks numbers.
Block numbering this number is the last possible for this block
pseudo interpolation 3 is the last possible for this corner, 10 on the other corner.