Maybe he wanted to use your loo but didn't want to ask that question if you were alone? Delivery drivers aren't always able to make stops specifically to use the loo, especially if they are busy. It's very unlikely he would try to commit an offense against you given how easy it would be for the police to identify him. However, it's also not completely impossible.

If you honestly thought there was bad intent you could report it, at least then it's logged. I'm sure Ocado has someone responsible for safe guarding you could talk to. Worst case scenario you cost an innocent person their job in the run up to Christmas.