To add to what ty already said: Yes, the wallet contains a seed, so that future private keys and their addresses can be derived deterministically. Unlike some other crypto wallets, Bitcoin Core and thus Xaya Core do not easily expose the seed (e.g. in form of a 12-word-sequence), but they have one nevertheless. Thus someone finding your USB stick can indeed recover also future addresses.
If you have the USB stick itself encrypted or have a wallet passphrase, then the wallet is safe unless the thief or finder can crack those passwords. But yeah, if I were you and just to be safe, I would create a new wallet and transfer everything there as ty has recommended. (And don't forget to make a new backup!)