Now I'm not sure if that was intended or not, but as a viewer we tend to have our own perceptions and yes those perceptions can be biased. I might be reading into the scene a lot more than was intended, but hey I think we all do that from time to time on this forum 😉
Anyhow moving on, not just the past, but I think it foreshadowed the ArSh relationship. I think we're all quite sure of the fact that Shilpa will be the first to fall in love with Armaan (a process that has started) whilst Armaan takes his time to move on and reciprocate her feelings. So I feel that Shilpa will give him a lot of love and care, while he rejects it. She will do a lot for him, but he will still be hung up in his "memory-istan". Hence the thanks for "everything". Moreover I think the Sajna tune further symbolizes this relationship that the two might share later on. The tune describes Shilpa's feelings for Armaan, and almost gives a sense of pain in return for the love given by Shilpa.
So that was my long rant on the three words said by Armaan, and knowing the creatives, as I mentioned before, I might be reading into it alot more than was intended. But seeing the current track and Star's recent updates, I do feel that I might be on the right track...