Use of iba for 'was' but not going

Question

Hello, 
I am reading a fairly reputable bilingual version of Sherlock Holmes. On one sentence it says 'Iba vestido discretamente con un traje de mezclilla de lana....'
The translation (and my own reading of the context) suggests that this means 'He was discretely dressed....'
But if that's the case why have they used 'iba'? Is that incorrect? The man was not 'going to do' anything. He just 'was'. My searching online and using Google translate suggests that only estar (or possibly ser) in the past tense are valid here, not ir.
Thanks!

Accepted Answer

Hola Ian
The verb ir (mainly in the present and the imperfect) is also used for description, where you'd normally use estar:
... iba vestido de payaso (he was dressed as a clown)
... va con unos zapatos rojos (he is wearing some red shoes)
... iba hecho un desastre (he was all a mess / looked like a mess)
... míralo, va totalmente borracho (look at him, he is completely drunk)
... iba mirando todos los escaparates... (he was looking at all the shop windows)
... va todo bien, gracias... (everything is going well, thanks)
The use of ir gives that extra nuance of progression - you can see the action in progress as opposed to the more static estar. 
Your example from Sherlock Holmes is using a past participle (vestido) but as you can see on these other examples, it could be used with a present participle, a whole phrase, or an adverb, for example. We have a lesson on this usage although it's focused on the use of ir with the present participle. Have a look here. I hope it helps.
Saludos cordiales
Inma

Answer

Inma thank you so much for your really helpful response. That makes sense now