Delta 248 to AMS diverted back to Detroit

Very new to the flighaware discussion forum, so please bare with me if I might come accross a bit naive; I am not a pilot or work in the industry, just an enthuziast.

I was going thru DTW airport last night on my way back from PHX to TVC and passed by the gate where DL248 B767-300 was boarding (and wanted to hop on that plane!!!). After I got home last night (after 11PM) just checked to see where about that plane was and I was shocked to see that it was divereted back to DTW. Could not find any explanation anywhere on the web why. It did leave again well after midnight. Anyone knows what might have happened???

Usually medical or mechanical.