Seeing as how PS4 and XBO have been pretty close to each other for the most part with PS4 being slightly ahead every month I don't see what's so different about May that would make XBO DRASTICALLY drop to the point where it's not even at 100k.
Except the PS4 hasn't only been slightly ahead. In just the first 4 months, the gap in the US grew by 500K. Last month the gap was ~100K. And it wouldn't really be a drastic drop for the XBO to drop below 100K. It only did ~107K last year. It would only take it being down 7% for it to drop below 100K.