This is the exactly true answer! This is normal business pract

This is normal business practice in most countries. It totally makes sense.

隻給我報銷在國內的機票, since the travel exp. in 國內 is for business purpose;
不給報銷回國的機票, since u were on vacation,來回中國的機票 exp. were for personal travel intention.

Think this way, if there was no such things of "拜見客戶", you at least pay the 來回中國的機票 exp by yourself.