Homeless people are just people lol. If he's just using it for water, it sounds like he watered your plants as a thank you? Idk, it doesn't sound particularly malicious, but I get the concern since he was on your property and close to your front door (I assume that's where your verandah is).

fill a water bottle

Or bong 🙃

Might be harmless, but also mental health or drugs could be involved so you never know. Wise to be cautious. Who knows what is in his head? Maybe he thinks your house is the one where the secret alien overlord plants live and he needs to water them to appease them. Someone with normal mental health does not go onto someone’s property to water plants late at night. It’s weird, somethings going on there.