How did this toad get here?

I live in a first floor flat with a huge communal, locked door, a long flight of stairs and of course my front door. Yet today I discovered a rather fat Common Toad in my hallway get batted around by my kitten. I'm sure the first thought would be the cat brought it in, but he's an indoor cat so that's impossible. I'm pretty confused as the nearest toad colonies are a good mile or two away and there are no ponds around here as it's just blocks of flats. There's a chance it squeezed under my front door, but it still doesn't explain tackling the main door and the stairs, I've kept many species of toad and know theyre not the most graceful of movers. Any ideas?