I don't believe there is any such word as 'densed'. 'Dense' is an adjective (eg dense forest') , 'densely' is the adverb (eg densely populated) , and 'density' is the noun (eg population density). I don't think that your friends were making a mistake, though. Perhaps you misheard what they said?

Hello, Zhenya! You're correct - if a place is described as being "dense", it must be filled with people or something else (e.g. a "dense" forest is filled with trees and vegetation) Unfortunately, I have not encountered the term "densed" and I don't think it is correct. "Dense" is not a verb (it is an adjective), which means that you cannot change its form into the different tenses. I hope this helps! :)

I can't think of a context where "densed" would be used. I cannot remember ever hearing anybody say that. Is it possible you are mishearing something else that they are saying?

Moreover, I have my right to ask them in person or ask here, or do whatever as long as it's what I do. And I don't want to tell anyone my personal details by explaining why did this, not that.

Because I can see them again only in the class next week. Well, why not I ask here then?