Buddhist Religious Pictures explained:

Rafa is seen in these photos making an offering of food to the monk is typical Thai-Buddhist ceremony called "Sai Bart" which is performed every early in the morning and also in special occasions. Generally, the monk just walk by and people need to ask them to stop then put food, flower.. into their arm bowls. People pay worship to the monk and the monk blesses them.

In this article / news they said that it's quite a special activity with 18 monks walked by and Rafa could perform very impressively as been advised. He's kneeling down all the time, taking off his shoes and his cap ,beautifully doing a "Wai" (put hands together at chest level to pay worship) ,performing everything right and with nice respect. He smiled with happiness after that.

Lieutenant general Poonpismai L., the lady who took care of Rafa said that Rafa's a very nice and simple guy who listened to her advice of practice with attention and did it beautifully. Rafa's kneeling for so long which was so cute to watch. She also told Rafa not forget to make a wish while doing "Sai Bart" to win Wimbledon easier next time.