This will sound crazy, but I am possibly familiar with this kind of a strange trip he is on.
I am just reading through this thread now---but it is like Deja Vu for me.
When my younger brother was about 21-22, he started doing very odd things. He once took an unexpected trip from SF Bay Area to Honolulu. He had my mom's emergency credit card she gave him in case of necessities.
And he did not contact us for a couple of days, but my mom saw notification of the one way airline ticket, and then a hotel charge. We began calling the hotel but he never called back.
I got one garbled message from him around day 5, saying he was 'looking for answers' and could not return home yet.
Needless to say, this trip was the beginning of our mental health awareness journey for my little brother and he was eventually diagnosed with schizophrenia.
Eventually the Honolulu police called my older brother---my little bro had his phone number in his jeans pocket. My bro was found, alive but beaten up, alone on a mountain trail. He did not remember what happened but he must have angered someone. My older brother flew to Hawaii and brought him back home after he recovered from his injuries.