If you used sanitizer in the airlock, it tends to get bubbly just with the air escaping. That doesn't necessarily mean that any yeast or mess is escaping. If you haven't seen the difference before, it can be easily confused.
Either way though, a blowoff tube is a cheap and easy way to ensure against a huge mess. I personally use them in every fermentation and just leave them on the whole time. The only time I switch to a airlock is if I have to open the fermenter to dryhop, take a final gravity reading etc