It's not just April's numbers, it's the general trends.
Wii U is dead and buried. It's got well over a year's track record at this point to give us reliable data.
Xbox One is trending absolutely terribly. It's not a dead system, but it's going to be a weaker second rather than a stronger one, based not just on sales this month but the curve of the sales over the first 6 months or so.
PS4 is doing well overall, not great this month. The 6 month curve is troubling and not particularly great for the leading console of a generation where both other competitors are weak.
That's what we're looking at here: not just this month's sales, but the shape of the sales curve so far in the 6 month (or 14 month history, for Wii U) of this young generation.