Is it true that on Saturn's moon Titan, you could walk around without a pressure suit, just heavy parka jacket and oxygen tanks?

Yes, it is true but for a very limited amount of time!

Titan atmosphere has 94.2% nitrogen, 5.65% methane and 0.099% hydrogen. The atmospheric pressure is 1.45 atm, so in theory it is possible to go outside without a pressured suit without problems for a short amount of time.

In other hand, temperature is around -179.2C on average. Human can survive at this temperature for just 1.1 minutes before it freeze you entirely. You can still enjoy a full 1 minute before get entirely frozen and you don’t need any kind of space suit.

But if you really want to stay out in this environment for an entire day, you will need oxygen tank and a special suit made using Aerogel materials that is best known by humans to insulate cold. You can still use 70% of the nitrogen available around mixing it with oxygen, so you can walk carrying a small tank. The low gravity will give you impression that you are stronger like a Dragon Ball Z fighter.