>Coming to an expensive first world country with $600 for 2 weeks is pretty clearly sketchy.
Bingo.
Entering the US with $5000 in Bitcoin would be equivalent to crossing the border with $5000 in Somaliland Shillings. They are both currencies that are bought and sold every day, but you can't take either to your neighborhood bank and convert them to USD. They have a very limited -- hell, even zero -- utility outside of circles that deal directly with them.
Bingo.
Entering the US with $5000 in Bitcoin would be equivalent to crossing the border with $5000 in Somaliland Shillings. They are both currencies that are bought and sold every day, but you can't take either to your neighborhood bank and convert them to USD. They have a very limited -- hell, even zero -- utility outside of circles that deal directly with them.
As such, CBP was rightly suspicious.