Aileen I did wonder whether playing in front of a smattering of people after the buzz of DC was a factor. Perhaps he was also adjusting to hard courts after clay (which I think is his best surface)? But as you say he didn't really look that engaged, which is a shame as he needs to be careful he doesn't fall further down the rankings and thereby not get automatic entry to such tournaments.
Missing the imposing presence of his mentor Andy, perhaps?
Probably a combination of all these, plus the absence of Leon (he might have been there of course but the cameras never focussed on the crowd), but I think the most important might have been that he just found it difficult to adjust to coming off the high of the DC tie. The sparseness and flatness of the crowd was certainly getting to me - and I was only watching! In fact the only time they really came to life was when local hero Diez won. The heat and humidity could have played its part as well.
Hopefully he'll do better in Rio, particularly as he'll be part of a team again.