So Titan's atmosphere is "hostile" ... but not actively so like the atmosphere of Venus (which is loaded with sulfuric acid).
With enough thermal insulation/protection (because Titan is COLD!), it would be possible to walk around in Titan's atmosphere without a pressure suit ... but you would still need to bring your own oxygen to breathe (because the atmosphere won't have useful enough quantities to work with).
And what you are describing in this case is explicitly
not a Type A atmosphere as it is put forth in the Traveller rules:
"Exotic atmospheres require the use of oxygen tanks, but protective suits are not required."
-- CT LBB 3 ('Worlds & Adventures'), page
This is a description of a simple inert or nontoxic reducing (anaerobic) environment. They are otherwise not hostile environments. You may not be able to breathe in it, but you are able to walk around otherwise unclad -- or at least in as little as local modesty rules and basic hygiene or comfort allow.
The average temperature on Titan, on the other hand, is -180c. There is no amount of exposed human skin that is safe under those conditions.
Hmmm ... let's see. What did I write that obviously wasn't comprehended?
So Titan's atmosphere is "hostile" ... but not actively so like the atmosphere of Venus (which is loaded with sulfuric acid).
Chemically speaking, if you warmed up Titan's atmosphere (to a nominal 15-25º C) through some kind of heat exchanger system, a human wouldn't be able to (usefully) breathe it due to a lack of O
2 in it. Therefore, you would need to bring your own (tanked) oxygen to breathe in Titan's atmosphere.
Exotic atmospheres require the use of oxygen tanks

With enough thermal insulation/protection (because Titan is COLD!), it would be possible to walk around in Titan's atmosphere without a pressure suit
That's a thermal problem, rather than an atmospheric pressure problem. In other words, a full on vacc suit is not necessarily required for a "pressure sealed environment" to keep a human alive.
Additionally, LBB3.81 was written at a time when ALL of the mainworlds represented by UWP codes were in the "habitable zone" and thus biased towards being survivable. The fact that Titan is a moon of an "outer orbit gas giant" located beyond the snow line in the Sol system wasn't a factor when LBB3.81 was being written and edited.
but protective suits are not required

If you step over the thermal issue (because outer system planetary orbit), Titan's atmosphere is not chemically hostile in an active way to machinery, technology and engineering, let alone human flesh. Titan's atmosphere will not chemically "destroy" stuff the same way (or at the same rate) that superheated sulfuric acid suspended in the atmosphere would. The hydrocarbon chemistry of Titan's atmosphere is "relatively benign" (code: A) compared to the sulfuric acid chemistry present in the atmosphere of Venus (code: B).
To take the analogy one step further, I would imagine that an atmosphere which is predominantly chlorine/fluorine would be code: B-C depending on chemical composition and how rapidly that atmospheric chemistry "attacks" machinery, technology and engineering (let alone human flesh).
Titan's atmosphere may "smell bad" and it may leave an unpleasant residue on anything moving around in it, but it isn't going to start DISSOLVING machines and people exposed to it.
The atmosphere of Venus, however ... IT HATES EVERYTHING ... especially down at the planetary surface (where everything gets "hot & melty"). Higher up in the Venusian atmosphere, where the pressure drops down to "Terra nominal" the temperature also drops to something "Terra nominal" but you're still looking at an atmosphere that is actively circulating sulfuric acid through it, so not only will it SMELL like rotten eggs (that distinctive sulfur smell) but it will also slowly EAT whatever is put there (in some kind of "floating city" context).
Sulfuric acid doesn't chemically "attack" everything, necessarily ... but there are an awful lot of materials and molecules that sulfuric acid "doesn't play nice with" ... so code: B Corrosive at the bare minimum.