Debojit has his very own unique voice. You can easily make out when he is singing. I feel every singer's voice texture may be suitable for certain songs better than others. Like, Abhijeet sung Manna dey's qawalli and it suited his voice texture very well. Similarly, certain songs suits Debojit's voice. And this includes the song he sang when Shekhar made that comment.
I feel it is not only the voice texture but How well you have mastered that song. If you can copy that song to the hilt and do all the harkatein in the original song, it would sound like the original. I think Shekhar's comments in the context of that particular song were true.If Debojit sounded most similar to Kishore Kumar compared to other singers can only be made out when you hear other's singing the same song.
The other day he reminded Shekhar of SP Balasubramanium when Debojit sang SP's song. Which may be true as Debojit's voice has that melodiousness of SP and mastering his song made it sound like him.
Shekhar made the comments in the contexts of those two songs and it make sense that way. Otherwise, Debojit is a very original singer.
They already crowned two singers one who won the K for Kishore and the other who is singing for Kishore Kumar character in the movie. But there were few songs where other singers sounded closest to Kishore.
I feel Debojit has a very unique and impressive personality and has a unique melodious voice and he don't need to be a copy cat.