Dan is playing well on grass. And it's definitely not the favoured surface of his opponent. Might be a good gamble.
It is arguably a good bet due to Falla's poor recent form but while grass is not his favourite surface he is actually pretty good on it.
In 2012 he reached the third round of Wimbledon beating Isner in R1 and Mahut in R2 and in 2014 he reached the final of Halle beating Kohlschrieber in the SF and then pushing Federer to two tie breaks in the final.